with whom Mr. Justice Brennan joins, concurring in part and dissenting in part.
I join the Court’s opinion to the extent that it holds that Exemption 7 (A) of the Freedom of Information Act (Act or FOIA), 5 U. S. C. § 552 (b) (7) (A) (1976 ed.), permits the federal courts to determine that “with respect to particular kinds of enforcement proceedings, disclosure of particular kinds of investigatory records while a case is pending would generally 'interfere with enforcement proceedings.’ ” Ante, at 236. *244I endorse the limitation of such “generic determinations of likely interference,” ibid., to “an imminent adjudicatory proceeding” that is “necessarily of a finite duration,” ante, at 229 n. 10. I also agree that the National Labor Relations Board (Board) has sustained its burden of justifying nondisclosure of statements by current employees that are unfavorable to their employer’s cause in an unfair labor practice proceeding against that employer. But I cannot accept the Court’s approval of the application of the Board’s rule of nondisclosure to all witness statements, unless and until a witness gives direct testimony before an administrative law judge. And I disagree with the Court’s apparent interpretation of Exemption 7 (A) as providing no “earlier or greater access” to records than that available under the discovery rules that an agency chooses to promulgate. See concurring opinion of Mr. Justice Stevens, ante, p. 243. There is no persuasive evidence that Congress in 1974 intended to authorize federal agencies to withhold all FOIA-requested material in pending proceedings by invoking restrictive rules of discovery promulgated under their “housekeeping” rulemaking authority.1
I
The starting point is the language of Exemption 7 (A). Congress provided for the nondisclosure of “investigatory records compiled for law enforcement purposes, but only to the extent that the production of such records would (A) interfere with enforcement proceedings . . . .” Establishing a presumption of disclosure, the Act “does not authorize withholding of information or limit the availability of records to the public, *245except as specifically stated in this section.” 5 U. S. C. § 552 (c) (1976 ed.). Moreover, “[a]ny reasonably segregable portion of a record shall be provided to any person requesting such record after deletion of the portions which are exempt under this subsection.” § 552 (b).
The language of Exemption 7 (A) simply cannot be squared with the Court's conclusion that “giving a party litigant earlier and greater access to the Board’s case than he would otherwise have” under agency rules is “the kind of harm that Congress believed would constitute an 'interference’ with NLRB enforcement proceedings . . . .” Ante, at 241. It is instructive to compare the 1974 amendment with the 1966 version of the “investigatory files” exemption. Exemption 7 as originally enacted permitted nondisclosure of “investigatory files compiled for law enforcement purposes except to the extent available by law to a private party.” 80 Stat. 251.2 Congress in 1974 abandoned the language that keyed the standard of disclosure to that available generally to private litigants.3 In its place, Congress prescribed that the withholding of investigatory records be based upon one or more of six specified types of harm. That change in language suggests that Congress may have intended a more focused inquiry into the likelihood of harm resulting from disclosure of investigatory records than was possible under a standard defining the scope of disclosure in terms of an agency’s rules of discovery.4
*246The Court of Appeals in this case observed that “[i]f the mere fact that one could not have obtained the document in private discovery were enough, the Board would have made naught of the requirement that nondisclosure be permitted ‘only to the extent that . . . production . . . would . . . interfere’ in some way” with the proceeding. 563 F. 2d 724, 730 (CA5 1977). There also is force to the Court of Appeals’ view that such a standard is unworkable because the courts have not accorded uniform recognition to the Board’s authority to deny rights of discovery to litigants in proceedings before it. Moreover, that court noted that a discovery standard may require an' assessment of the particular needs of the FOIA plaintiff when the Act mandates release of information “to any person,” 5 U. S. C. § 552 (a)(3) (1976 ed.), incorporating the principle that “anyone’s case is as strong (or as weak) as *247anyone else’s.” 563 F. 2d, at 730; see NLRB v. Sears, Roebuck & Co., 421 U. S. 132, 143 n. 10 (1975).
Nor does the legislative history provide more than ambiguous support for the Court’s reading. There are statements by Senator Hart, the principal sponsor of the Exemption 7 amendment, that appear favorable. But these statements, made on the floor of the Senate, are not very clear on the point in dispute. Thus while Senator Hart noted that the original intent of the 1966 provision was to deny “an opposing litigant earlier or greater access to investigative files than he would otherwise have,” 120 Cong. Rec. 17033 (1974), reprinted in 1975 Source Book 332, he also said that Exemption 7 (A) “would apply whenever the Government’s case in court— a concrete prospective enforcement proceeding — would be harmed by the premature release of evidence or information not in the possession of known or potential defendants.” Id., at 333. If Exemption 7 (A) were intended to authorize nondisclosure in every pending proceeding, it is doubtful that Senator Hart would have spoken in terms of “whenever the Government’s case in court . . . would be harmed by the premature release . . . .” I find equally unilluminating statements to the effect that the 1974 amendment was not intended to work “a radical departure from existing case law under the Freedom of Information Act.” Id., at 334 (remarks of Sen. Hart).
The one point that emerges with clarity is that Congress intended that “the courts look ... to the reasons for the seventh exemption before allowing the withholding of documents.” Ibid. But it is difficult to reconcile that principle with the underlying rationale of the Court’s opinion that “the release of information in investigatory files prior to the completion of an actual, contemplated enforcement proceeding was precisely the kind of interference that Congress continued to want to protect against.” Ante, at 232. Congress had before it several proposals that would have drawn the line between *248files in “pending or contemplated” proceedings and files in “closed” cases. These were not adopted.5 One must assume that a deliberate policy decision informed Congress’ rejection of these alternatives in favor of the language presently contained in Exemption 7 (A). Moreover, as the Court notes, ante, at 229 n. 10, at least two of the decisions of the Court of Appeals for the District of Columbia Circuit that Congress intended to overrule “involved files in still-pending investigations.” See Ditlow v. Brinegar, 161 U. S. App. D. C. 154, 494 F. 2d 1073, cert. denied, 419 U. S. 974 (1974); Center for National Policy Review v. Weinberger, 163 U. S. App. D. C. 368, 502 E. 2d 370 (1974).6 Senator Hart stated that these cases, among others, were wrongly decided because the courts failed to approach the disclosure issue “on a balancing basis, which is exactly what this amendment seeks to do.” 1975 Source Book 349.
The Court’s approach in this case also is in tension with Congress’ most recent amendment to the Act. Congress in 1976 overturned our decision in FAA Administrator v. Robertson, 422 U. S. 255 (1975), which held that Exemption 3, 5 U. S. C. § 552 (b) (3), should not be interpreted to disturb a broad delegation of authority to an agency to withhold information from the public. Pub. L. No. 9-N409, § 5 (b) (3), 90 Stat. 1247. Congress tightened the standard for Exemp*249tion 3 “to exempt only material required to be withheld from the public by any statute establishing particular criteria or referring to particular types of information,” and rejected Robertson, which was viewed as “afford [ing] the FAA Administrator cart[e] blanche to withhold any information he pleases ...” H. R. Rep. No. 94^880, pt. 1, p. 23 (1976). The Court's ruling today appears to afford an agency similar carte blanche authority to withhold witness statements in investigatory files, at least during the pendency of an enforcement proceeding.
The Court appropriately recognizes the danger that FOIA claims are “likely to cause substantial delays in the adjudication of unfair labor practice charges.” Ante, at 237-238. But Congress had a right to insist, as I believe it did in the 1974 legislation, that nondisclosure of investigatory records be grounded in one of the six specific categories of harm set out in Exemption 7, even though litigation may ensue over disputed claims of exemption.
II
As the Court demonstrates, the congressional requirement of a specific showing of harm does not prevent determinations of likely harm with respect to prehearing release of particular categories of documents. The statements of the Act’s sponsors in urging an override of President Ford’s veto of the 1974 amendments shed light on this point. The President’s message to Congress explained that “confidentiality would not be maintained if many millions of pages of FBI and other investigatory law enforcement files would be subject to compulsory disclosure at the behest of any person unless the Government could prove to a court — separately for each paragraph of each document — that disclosure 'would’ cause a type of harm specified in the amendment.” 1975 Source Book 484. The bill’s proponents discounted the President’s concern. See id., at 405-406 (remarks of Rep. Moorhead); id., at 451-452 *250(remarks of Sen. Hart). As then Attorney General Levi observed: “This legislative history suggests that denial can be based upon a reasonable possibility, in view of the circumstances, that one of the six enumerated consequences would result from disclosure.” Attorney General’s Memorandum on the 1974 Amendments to the Freedom of Information Act-13 (1975), reprinted in 1975 Source Book 523.
A
In my view, the Board has demonstrated a “reasonable possibility” that harm will result from prehearing disclosure of statements by current employees that are damaging to their employer’s case in an unfair labor practice proceeding. The Courts of Appeals have recognized with virtual unanimity that due to the “peculiar character of labor litigation[,] the witnesses are especially likely to be inhibited by fear of the employer’s or — in some cases — the union’s capacity for reprisal and harassment.” Roger J. Au & Son, Inc. v. NLRB, 538 F. 2d 80, 83 (CA3 1976).7 The “delicate” relationship between employer and employee — or between union and employee-member — suggests that “[t]he labor case is peculiarly susceptible to employer [or union] retaliation, coercion, or influence to the point that it can be concluded that there is no need for an express showing of interference in each case to justify giving effect to the exemption contained in Section 7 (A) in *251Labor Board proceedings.” Climax Molybdenum Co. v. NLRB, 539 F. 2d 63, 65 (CA10 1976).
The Board knows from experience that an employer or a union charged with an unfair labor practice often can exercise special influence — either through threats or promises of benefit — over employees or members whose welfare and opportunity for advancement depend on remaining in the good graces of the charged party. Accordingly, the Court has construed § 8 (a) (4) of the National Labor Relations Act, as amended, 61 Stat. 140, 29 U. S. C. § 158 (a)(4), to protect employees who give written sworn statements to a Board field examiner even when they do not file a charge or testify at a formal hearing on the charge. NLRB v. Scrivener, 405 U. S. 117 (1972).8
Although the Board may be able to impose post hoc sanctions for interference with its witnesses, see 29 U. S. C. §§ 158 (a)(4) and 162; 18 U. S. C. § 1505 (1976 ed.), these remedies cannot safeguard fully the integrity of ongoing unfair labor practice proceedings. Intimidation or promise of benefit may be subtle and not susceptible of proof. As the Board cannot proceed without a charge filed by knowledgeable individuals, see Nash v. Florida Industrial Comm’n, 389 U. S. 235, 238 (1967), many instances of interference could go undetected. Even if interference is detected and a complaint is filed, appropriate sanctions often cannot be imposed until after the initial unfair labor practice proceeding has terminated. Moreover, as the Court notes, many employees, mindful of the *252Board’s prehearing settlement practice, may be willing to cooperate with the Board because they know that their identity will not be revealed and they will not be called to give public testimony adverse to their employer’s interest unless such a course is absolutely necessary.
Until the Board’s view here is proved unfounded, as an empirical matter, I agree that the danger of altered testimony' — ■ through intimidation or promise of benefit — provides sufficient justification for the judgment that disclosure of unfavorable statements by current employees prior to the time when they are called to give testimony before an administrative law judge, “would interfere with enforcement proceedings . 9
B
But the Court holds that all “witness statements in pending unfair labor practice proceedings are exempt from FOIA disclosure at least until completion of the Board’s hearing. . . .” Ante, at 236. I find no warrant for that sweeping conclusion in the expressed intention of the 93d Congress. Exemption 7 (A) requires that the Board demonstrate a reasonable possibility that disclosure would “interfere with enforcement proceedings . . . .” In my view, absent a particularized showing of likely interference, statements of all witnesses — other than current employees in proceedings against employers (or union members in proceedings against unions) — are subject to the statutory presumption in favor of disclosure. In contrast to the situation of current employees or union members, there simply is no basis for presuming a particular likelihood of employer interference with union representatives or others not employed by the charged party, or, in a proceeding against a union, of union interference with employer representatives and other nonmembers of the union or the bargaining unit. Simi*253larly, I am unwilling to presume interference with respect to disclosure of favorable statements by current employees, and would require the Board to show a reasonable possibility of employer reprisal. See Temple-Eastex, Inc. v. NLRB, 410 F. Supp. 183, 186 (ED Tex. 1976).
I do not read the Act to authorize agencies to adopt or adhere to nonstatutory rules10 barring all prehearing disclosure of investigatory records. The Court reasons, ante, at 241, that such disclosure — which is deemed “premature” only because it is in advance of the time of release set by the agency — will enable “suspected violators ... to learn the Board’s case in advance and frustrate the proceedings or construct defenses which would permit violations to go unremedied . . . .” Title Guarantee Co. v. NLRB, 534 F. 2d 484, 491 (CA2), cert. denied, 429 U. S. 834 (1976). This assumption is not only inconsistent with the congressional judgment expressed in the Federal Rules of Civil Procedure that “trial by ambush,” New England Medical Center Hosp. v. NLRB, 548 F. 2d 377, 387 (CA1 1976); Capital Cities Communications, Inc. v. NLRB, 409 F. Supp. 971, 977 (ND Cal. 1976), well may disserve the cause of truth, but it also threatens to undermine the Act’s overall presumption of disclosure, at least during the pendency of enforcement proceedings.11
*254There may be exceptional cases that would permit the Board to withhold all witness statements for the duration of an unfair labor practice proceeding. Such a situation could arise where prehearing revelation would divulge incompletely developed information which, if prematurely disclosed, may interfere with the proceedings before the Board, or where the facts of a case suggest a strong likelihood that the charged party will attempt to interfere with any and all of the Board’s witnesses. The Act requires, however, that the Board convince a federal court that there is a reasonable possibility of this kind of interference.12
I would reverse the judgment of the Court of Appeals to the extent that it requires prehearing disclosure of unfavorable statements by respondent’s current employees, but affirm as to any remaining statements in dispute.13
The FOIA was enacted in 1966 as a remedy for agency “housekeeping” rales that had restricted unduly public information about the operations of Government. See H. R. Rep. No. 1497, 89th Cong., 2d Sess., 3-6 (1966); S. Rep. No. 813, 89th Cong., 1st Sess., 3, 5 (1965). Congress intended to establish legislative standards for nondisclosure of official information and to empower the federal courts to review claims of agency noncompliance with those standards.
The exception clause first appeared in a post-passage amendment on the floor of the Senate to accommodate Senator Humphrey’s desire that the investigatory files exemption shield from disclosure prehearing statements of NLRB witnesses. 110 Cong. Rec. 17666-17668 (1964), reprinted in Subcommittee on Administrative Practice and Procedure, Senate Judiciary Committee, Freedom of Information Act Source Book, S. Doc. No. 93-82, pp. 109, 111 (1974).
Congress did not disturb similar language contained in Exemption 5, 5 U. S. C. § 552 (b) (5) (1976 ed.). See EPA v. Mink, 410 U. S. 73, 85-86 (1973).
Although the Committee Reports and the debates appear to be silent on *246the point, the deletion of the exception clause has been viewed as evidence of an intent to broaden the scope of disclosure under Exemption 7. See Fuselier & Moeller, NLRB Investigatory Records: Disclosure Under the Freedom of Information Act, 10 U. Rich. L. Rev. 541, 546 (1976). Others have attached little significance to this change in language. See Attorney General’s Memorandum on the 1974 Amendments to the Freedom of Information Act 5 n. 3 (1975), reprinted in House Committee on Government Operations and Senate Committee on the Judiciary, Freedom of Information Act and Amendments of 1974 (Pub. L. 93-502) Source Book, 94th Cong., 1st Sess., 515 (Joint Comm. Print 1975) (hereinafter cited as 1975 Source Book); Ellsworth, Amended Exemption 7 of the Freedom of Information Act, 25 Am. U. L. Rev. 37, 45-46, n. 39 (1975). In an early decision, the clause had been construed “to limit persons charged with violations of federal regulatory statutes to the discovery available to persons charged with violations of federal criminal law.” Bristol-Myers Co. v. FTC, 138 U. S. App. D. C. 22, 26, 424 F. 2d 935, 939, cert. denied, 400 U. S. 824 (1970). See Note, The Freedom of Information Act: A Seven-Year Assessment, 74 Colum. L. Rev. 895, 948, and n. 291 (1974). The proviso later was relied on by the same court to deny disclosure to an FOIA litigant who would not have been a “party” engaged in litigation with an agency. See Weisberg v. United States Dept. of Justice, 160 U. S. App. D. C. 71, 79 n. 15, 489 F. 2d 3195, 1203 n. 15 (1973) (en banc), cert. denied, 416 U. S. 993 (1974).
See 2 Hearings on S. 1142 et al. before the Subcommittees on Administrative Practice and Procedure and Separation of Powers of the Senate Judiciary Committee and the Subcommittee on Intergovernmental Relations of the Senate Committee on Government Operations, 93d Cong., 1st Sess., 2 (1973) (Sen. Kennedy); id., at 227 (Dept, of Justice), discussed in 1975 Source Book 339; id., at 338 (Committee on Federal Legislation of the Assn, of Bar of City of New York).
In Center for National Policy Review, for example, the court held that Exemption 7 permitted the Secretary of Health, Education, and Welfare to resist disclosure of the material of 22 "open and active” files involving agency review of public school discrimination practices in northern localities.
The Court of Appeals in this case also recognized that “there may be some risk of interference with Board proceedings in the form of witness intimidation from harassment of an employee-witness during the five days prior to the hearing, done in an effort to silence him or dilute the nature of his testimony.” 563 F. 2d 724, 732 (CA5 1977). It determined, however, that the Board had failed to introduce any evidence tending to show that such intimidation was likely, and declined to accept the Board’s assertion that “in every case the potential for intimidation is so great as to require nondisclosure of all statements and affidavits.” Id,., at 732-733 (emphasis supplied).
The Court’s substantive labor law rulings have “take[n] into account the economic dependence of the .employees on their employers, and the necessary tendency of the former, because of that relationship, to pick up intended implications of the latter that might be more readily dismissed by a more disinterested ear.” NLRB v. Gissel Packing Co., 395 U. S. 575, 617 (1969); see Textile Workers v. Darlington Co., 380 U. S. 263 (1965); NLRB v. Exchange Parts Co., 375 U. S. 405 (1964). Similar considerations apply to statements made or inducements offered by labor unions. See, e. g., NLRB v. Savair Mfg. Co., 414 U. S. 270 (1973).
Similarly, the Board may protect against prehearing disclosure statements by union members and employees unfavorable to the union’s cause in an unfair labor practice proceeding.
It may be that criminal law enforcement agencies will be able to resist pretrial disclosure of witness statements on the theory that the Jencks Act, 18 U. S. C. §3500 (a) (1976 ed.), falls within the terms of Exemption 3 of the Act; see supra, at 248-249.
1 do not construe the Court’s ruling today to authorize agencies to withhold disclosure of materials generated in closed or otherwise inactive proceedings, absent a particularized showing of harm, even though the Board itself would like this authority. Brief for Petitioner 33 n. 17. The Board has advanced this view in the Courts of Appeals with some success. Compare New England Medical Center Hosp. v. NLRB, 548 F. 2d, at 385-386 (records generated in a related, inactive investigation held protected against disclosure), with Poss v. NLRB, 565 F. 2d 654, 657 (CA10 1977) (statements taken in an investigation that ended in a decision not to issue a complaint held not protected).
In light of my view of the limits of Exemption 7 (A), I reach the Board's alternative argument that the witness affidavits in dispute are protected against disclosure by Exemption 5, 5 U. S. C. § 552 (b) (5) (1976 ed.). That section provides that the Act does not apply to "inter-agency or intra-agency memorandums or letters which would not be available by law to a party other than any agency in litigation with the agency. ...” I agree generally with the analysis of the Court of Appeals that the purpose of this Exemption is to protect agency litigation strategy and decisionmaking processes, and not to incorporate fully the “work product” privilege recognized in Hickman v. Taylor, 329 U. S. 495 (1947), and Fed. Rule Civ. Proc. 26 (b)(3). Our decision in NLRB v. Sears, Roebuck & Co., 421 U. S. 132, 154-155, 159-160 (1975), provides support for this view. In this case, by contrast, the Board does not suggest that the witness affidavits in question are anything other than verbatim transcripts of statements made by witnesses to Board personnel.
There is no need for a remand in this case, cf. Harvey’s Wagon Wheel, Inc. v. NLRB, 550 F. 2d 1139, 1143 (CA9 1976), for the Board conceded in the District Court that “[t] here's nothing unique in Board proceedings in these statements App. 91.