.

Mr. Justice WHITE delivered the opinion of the Court.

    Section 8(a) of the Occupational Safety and Health Act of 1970 (OSHA or Act) empowers agents of the Secretary of Labor (Secretary) to search the work area of any employment facility within the Act's jurisdiction.  The purpose of the search is to inspect for safety hazards or violations of OSHA regulations.  No search warrant or other process is expressly required under the Act.

    On the morning of September 11, 1975, an OSHA inspector entered the customer service area of Barlow's, Inc., an electrical and plumbing installation business located in Pocatello, Idaho.  The president and general manager, Ferrol G. "Bill" Barlow, was on hand; and the OSHA inspector, after showing his credentials, informed Mr. Barlow that he wished to conduct a search of the working area of his business.  Mr. Barlow inquired whether any com-plaint had been received about his company. The inspector answered no, but that Barlow's, Inc., had simply turned up in the agency's selection process. The inspector again asked to enter the nonpublic area of the business; Mr. Barlow's response was to inquire whether the inspector had a search warrant. The inspector had none.  Thereupon, Mr. Barlow refused the inspector admission to the employee area of his business.  He said he was relying on his rights as guaranteed by the Fourth Amendment of the United States Constitution.

    Three months later, the Secretary petitioned the United States District Court for the District of Idaho to issue an order compelling Mr. Barlow to admit the inspector.  The requested order was issued on December 30, 1975, and was presented to Mr. Barlow on January 5, 1976.  Mr. Barlow again refused admission, and he sought his own injunctive relief against the warrantless searches assertedly permitted by OSHA.  A three-judge court was convened.  On December 30, 1976, it ruled in Mr. Barlow's favor. 424 F.Supp. 437.  Concluding that Camara v.  Municipal  Court, 387 US 523, 87 S.Ct. 1727, 1730, 1731, 18 L.Ed.2d. 930 (1967), and See v.  City of Seattle, 387 US 541, 87 S.Ct. 1737, 1739, 18 L.Ed.2d. 943 (1967), controlled this case, the court held that the Fourth Amendment required a warrant for the type of search involved here and that the statutory authorization for warrantless inspections was unconstitutional.  An injunction against searches or inspection pursuant to Section 8(a) was entered.  The Secretary appealed, challenging the judgment  . . . .

    The Secretary urges that warrantless inspections to enforce OSHA are reasonable within the meaning of the Fourth Amendment.  Among other things, he relies on Section 8(a) of the Act, +++ which authorizes inspection of business premises without a warrant and which the Secretary urges represents a congressional construction of the Fourth Amendment that the courts should not reject.  Regrettably we are unable to agree.

    The Warrant Clause of the Fourth Amendment protects commercial buildings as well as private homes.  To hold otherwise would belie the origin of that Amendment, and the American colonial experience.  An important forerunner of the first 10 Amendments to the United States Constitution, the Virginia Bill of Rights, specifically opposed "general warrants, whereby an officer or messenger may be commanded to search suspected places without evidence of a fact committed."  The general warrant was a recurring point of contention in the Colonies immediately preceding the Revolution.  The particular offensiveness it engendered was acutely felt by the merchants and businessmen whose premises and products were inspected for compliance with several parliamentary revenue measures that most irritated the colonists.  "[T]he Fourth Amendment's commands grew in large measure out of the colonists' experience with the writs of assistance . . . [that] granted sweeping power to customs officials and other agents of the King to search at large for smuggled goods." +++  Against this background, it is untenable that the ban on warrantless searches was not intended to shield places of business as well as of residences.

    This Court has already held that warrantless searches are generally unreasonable, and that this rule applies to commercial premises as well as homes.  In Camara v.  Municipal Court, supra, 387 US 528-529, we held:
"[E]xcept in certain carefully defined classes of cases, a search of private property without proper consent is 'unreasonable' unless it has been authorized by a valid search warrant."
On the same day, we also ruled:

"As we explained in Camara, a search of private homes is presumptively unreasonable if conducted without a warrant.  The businessman, like the occupant of a residence, has a constitutional right to go about his business free from unreasonable official entries upon his private commercial property.  The businessman too, has that right placed in jeopardy if the decision to enter and inspect for violation of regulatory laws can be made and enforced by the inspector in the field without official authority evidenced by a warrant."  See v.  City of Seattle, supra, 387 US 543.

    The Secretary urges that an exception from the search warrant requirement  has been recognized for "pervasively regulated business[es]," United States v.  Biswell, 406 US 311, 316 (1972) and for "closely regulated" industries "long subject to close supervision and inspection." Colonnade Catering Corp. v. United States, 397 US 72, 74, 77 (1970).  These cases are indeed exceptions, but they represent responses to relatively unique circumstances.  Certain industries have such a history of government oversight that no reasonable expectation of privacy, +++ could exist for a proprietor over the stock of such an enterprise.  Liquor (Colonnade) and firearms (Biswell) are industries of this type; when an entrepreneur embarks upon such a business, he has voluntarily chosen to subject himself to a full arsenal of governmental regulation.

    Industries such as these fall within the "certain carefully defined classes of cases," referenced in Camara, 387 US 528.  The element that distinguishes these enterprises from ordinary business is a long tradition of close government supervision, of which any person who chooses to enter such a business must already be aware.  "A central difference between those cases [Colonnade and Biswell] and this one is that businessmen engaged in such federally licensed and regulated enterprises accept the burdens as well as the benefits of their trade, whereas the petitioner here was not engaged in any regulated or licensed business.  The businessman in a regulated industry in effect consents to the restrictions placed upon him.

    The clear import of our cases is that the closely regulated industry of the type involved in Colonnade and Biswell is the exception.  The Secretary would make it the rule.  Involving the Walsh-Healy Act of 1936, the Secretary attempts to support a conclusion that all businesses involved in interstate commerce have long been subjected to close supervision of employee safety and health conditions.  But the degree of federal involvement in employee working circumstances has never been of the order of specificity and pervasiveness that OSHA mandates.  It is quite unconvincing to argue that the imposition of minimum wages and maximum hours on employers who contracted with the Government under the Walsh-Healy Act prepared the entirety of American interstate commerce for regulation of working conditions to the minutest detail.  Nor can any but the most fictional sense of voluntary consent to later searches be found in the single fact that one conducts business affecting interstate commerce; under current practice and law, few businesses can be conducted without having some effect on interstate commerce.

    The critical fact in this case is that entry over Mr. Barlow's objection is being sought by a Government agent.¹  Employees are not prohibited from reporting OSHA violations.  What they observe in their daily functions is undoubtedly beyond the employer's reasonable expectation of privacy.  The Government inspector, however, is not an employee.  Without a warrant he stands in no better position than a member of the public.  What is observable by the public is observable, without a warrant, by the Government inspector as well.  The owner of a business has not, by the necessary utilization of employees in his operation, thrown open the areas where employees alone are permitted to the warrantless scrutiny of Government agents.  That an employee is free to report, and the Government is free to use, any evidence of noncompliance with OSHA that the employee observes furnishes no justification for federal agents to enter a place of business from which the public is restricted and to conduct their own warrantless search.

    The Secretary nevertheless stoutly argues that the enforcement scheme of the Act requires warrantless searches, and that the restrictions on search discretion contained in the Act and its regulations already protect as much privacy as a warrant would.  The Secretary thereby asserts the actual reasonableness of OSHA searches, whatever the general rule against warrantless searches might be.  Because "reasonableness is still the ultimate standard,"Camara v.  Municipal Court, 387 US 539, the Secretary suggests that the Court decide whether a warrant is needed by arriving at a sensible balance between the administrative necessities of OSHA inspections and the incremental protection of privacy of business owners a warrant would afford.  He suggests that only a decision exempting OSHA inspections from the Warrant Clause would give "full recognition to the competing public and private interests here at stake."  Ibid.

    The Secretary submits that warrantless inspections are essential to the proper enforcement of OSHA, because they afford the opportunity to inspect without prior notice and hence to preserve the advantage of surprise.  While the dangerous conditions outlawed by the Act include structural defects that cannot be quickly hidden or remedied, the Act also regulates a myriad of safety details that may be amenable to speedy alteration or disguise.  The risk is that during the interval between an inspector's initial request to search a plant and his procuring a warrant following an owner's refusal of permission, violations of this latter type could be corrected and thus escape the inspector's notice.  To the suggestion that warrants may be issued exparte and executed without delay and without prior notice, thereby preserving the element of surprise, the Secretary expresses concern for the administrative strain that would be experienced by the inspection system, and by the courts, should exparte warrants issued in advance become standard practice.

    We are unconvinced, however, that requiring warrants to inspect will impose serious burdens on the inspection system or the courts, will prevent inspection necessary to enforce the statute, or will make them less effective.  In the first place, the great majority of businessmen can be expected in normal course to consent to inspection without warrant; the Secretary has not brought to this Court's attention any widespread pattern of refusal.²  In those cases where an owner does insist on a warrant, the Secretary argues that inspection efficiency will be impeded by the advance notice and delay.  The Act's penalty provision for giving advance notice of a search, and the Secretary's own regulations, indicate that surprise searches are indeed contemplated.  However, the Secretary has also promulgated a regulation providing that upon refusal to permit an inspector to enter the property or to complete his inspection, the inspector shall attempt to ascertain the reasons for the refusal and report to his superior, who shall "promptly take appropriate action, including compulsory process, if necessary." 29 CFR Sec. 1903.4 (1977).  The regulation represents a choice to proceed by process where entry is refused; and on the basis of evidence available from present practice, the Act's effectiveness has not been crippled by providing those owners who wish to refuse an initial requested entry with a time lapse while the inspector obtains the necessary process.³  Indeed, the kind of process sought in this case and apparently anticipated by the regulation provides notice to the business operator.  If this safeguard endangers the efficient administration of OSHA, the Secretary should never have adopted it, particularly when the Act does not require it.  Nor is it immediately apparent why the advantages of surprise would be lost if after being refused entry, procedures were available for the Secretary to seek an exparte warrant and reappear at the premises without further notice to the establishment being inspected.

    Whether the Secretary proceeds to secure a warrant or other process, with or without prior notice, his entitlement to inspect will not depend on his demonstrating probable cause to believe that conditions in violation of OSHA exist on the premises.  Probable cause in the criminal law sense is not required.  For purposes of an administrative search such as this, probable cause justifying the issuance of a warrant may be based not only on specific evidence of an existing violation⁴ but also on a showing that "reasonable legislative or administrative standards for conducting an . . . inspection are satisfied with respect to a particular [establishment].  "Camara v.  Municipal Court, 387 US 538.  A warrant showing that a specific business has been chosen for an OSHA search on the basis of a general administrative plan for the enforcement of the Act derived from neutral sources such as, for example, dispersion of employees in various types of industries across a given area, and the desired frequency of searches in any of the lesser divisions of the area, would protect the employer's Fourth Amendment rights.⁵  We doubt that the consumption of enforcement energies in the obtaining of such warrants will exceed manageable proportions.

    Finally the Secretary urges that requiring a warrant for OSHA inspectors will mean that, as a practical matter, warrantless search provisions in other regulatory statutes are also constitutionally infirm.  The reasonableness of a warrantless search, however, will depend upon the specific enforcement needs and privacy guarantees of each statute.  Some of the statutes cited apply only to a single industry, where regulations might already be so pervasive that a Colonnade Biswell exception to the warrant requirement could apply.  Some statutes already envision resort to federal court enforcement when entry is refused, employing specific language in some cases and general language in others.  In short, we base today's opinion on the facts and law concerned with OSHA and do not retreat from a holding appropriate to that statute because of its real or imagined effect on other, different administrative schemes.

    Nor do we agree that the incremental protection afforded the employer's privacy by a warrant are so marginal that they fail to justify the administrative burdens that may be entailed.  The authority to make warrantless searches devolves almost unbridled discretion upon executive and administrative officers, particularly those in the field, as to when to search and whom to search.  A warrant, by contrast would provide assurances from a neutral officer that the inspection is reasonable under the Constitution, is authorized by statute, and is pursuant to an administrative plan containing specific neutral criteria.⁶  Also, a warrant would then and there advise the owner of the scope and objects of the search, beyond which limits the inspector is not expected to proceed.  These are important functions for a warrant to perform, functions which underlie the Court's prior decisions that the Warrant Clause applies to inspections for compliance with regulatory statues.⁷ Camara v. Municipal Court, 387 US 523 (1967);  See v.  City of Seattle, 387 US 541 (1967).   We conclude that the concerns expressed by the Secretary do not suffice to justify warrantless inspections under OSHA or vitiate the general constitutional requirement that for a search to be reasonable a warrant must be obtained.

    We hold that Barlow's was entitled to a declaratory judgment that the Act is uncon-stitutional insofar as it purports to authorize inspections without warrant or its equivalent and to an injunction enjoining the Act's enforcement to that extent.  The judgment of the District Court is therefore affirmed.

So ordered.

________________________________
1  The Government has asked that Mr. Barlow be ordered to show cause why he should not be held in contempt for refusing to honor the inspection order, and its position is that the OSHA inspector is now entitled to enter at once, over  Mr. Barlow's objection.
2  We recognize that today's holding itself might have an impact on whether owners choose to resist requested searches; we can only await the development of evidence not present on this record to determine how serious an impediment to effective enforcement this might be.
3  A change in the language of the Compliance Operations Manual for OSHA inspectors supports the inference that, whatever the Act's administrators might have thought at the start, it was eventually concluded that enforce-ment efficiency would not be jeopardized by permitting employers to refuse entry, at least until the inspector obtained compulsory process.  The 1972 Manual included a section specifically directed to obtaining "warrants", and one provision of that section dealt with exparte warrants:

 "In cases where a refusal of entry is to be expected from past performance of the employer, or where the employer has given some indication prior to the commencement of the investigation of his intention to bar entry or limit to interfere with the investigation, a warrant should be obtained before the inspection is attempted.  Cases of this nature should also be referred through the Area Director to the appropriate Regional Solicitor and the Regional Administrator alerted." Dept. of Labor, OSHA Compliance Operations Manual V-7 (JAN. 1972).