discretion has generally been sustained by the lower courts.1o A profound alteration in the Board's trial strategy in unfair labor practice cases would thus be effectuated if the Board were required, in every case in which witnesses' statements were sought under FOIA prior to an unfair labor practice proceeding, to make a particularized showing that release of these statements would interfere with the proceeding."

Not only would this change the substantive discovery rules, but it would do so through mechanisms likely to cause substantial delays in the adjudication of unfair labor practice

16 Section 6 of the NLRA provides that the Board may "make such rules and regulations as may be necessary to carry out the provisions of this Act." Most Circuits have held that prehearing discovery questions are committed to the Board's discretion. See, e. g., NLRB v. Vapor Blast Mfg. Co., 287 F. 2d 402 (CA7 1961); Electromec Design & Development Co. v. NLRB, 409 F. 2d 631, 635 (CA9 1969); NLRB v. Interboro Contractors, Inc., 432 F. 2d 854, 858 (CA2 1970), cert. denied, 402 U. S. 915 (1971); D'Youville Manor, Lowell, Mass., Inc. v. NLRB, 526 F. 2d 3, 7 (CA1 1975); NLRB v. Valley Mold Co., 530 F. 2d 693, 695 (CA6 1976).

Contrary to these authorities, the Fifth Circuit has held that "when good cause is shown [the NLRB] should permit discovery" in unfair labor practice proceedings. NLRB v. Rex Disposables, 494 F. 2d 588, 592 (1974), citing NLRB v. Safway Steel Scaffolds Co., 383 F. 2d 273 (CA5 1967), cert. denied, 390 U. S. 955 (1968) (relying on § 10 (b) of the NLRA, 29 U. S. C. § 160 (b)). This view of discovery in Board proceedings may have influenced the decision of the court below, since it noted that, under the Fifth Circuit's approach to NLRB discovery, granting the FOIA request here might not have given the employer any more information about the Board's case than it could otherwise have obtained. Since the court below did not rest on this ground, but instead indicated that the prospect of premature revelation of the Board's case was not, of itself, an "interference" with enforcement proceedings, see supra, at 218, we intimate no view as to the validity of the Fifth Circuit's approach to Board discovery.

17 If the Court of Appeals' ruling below were not reversed, the Board anticipated that prehearing requests for witnesses' statements under FOIA would be made by employer-respondents in virtually all unfair labor practice proceedings. See Pet. for Cert. 9.

charges.18 In addition to having a duty under FOIA to provide public access to its processess, the NLRB is charged with the duty of effectively investigating and prosecuting violations of the labor laws. See 29 U. S. C. §§ 160, 161. To meet its latter duty, the Board can be expected to continue to claim exemptions with regard to prehearing FOIA discovery requests, and numerous court contests will thereby ensue. Unlike ordinary discovery contests, where rulings are generally not appealable until the conclusion of the proceedings, an agency's denial of a FOIA request is immediately reviewable in the district court, and the district court's decision can then be reviewed in the court of appeals. The potential for delay and for restructuring of the NLRB's routine adjudications of unfair labor practice charges from requests like respondent's is thus not insubstantial. See n. 17, supra.

In the absence of clear congressional direction to the contrary, we should be hesitant under ordinary circumstances to interpret an ambiguous statute to create such dislocations. Not only is such direction lacking, but Congress in 1966 was particularly concerned that premature production of witnesses' statements in NLRB proceedings would adversely affect that agency's ability to prosecute violations of the NLRA, and, as indicated above, the legislative history of the 1974 amendments affords no basis for concluding that Con

18 We believe that delay of adjudicatory proceedings is a relevant factor, because Exemption 7 requires us to look at the interference that would flow from the "production," and not merely the disclosure, of records. Since Congress had before it proposals that would have exempted only those investigatory records whose "disclosure" would create specified harms, see 1975 Source Book 338 (proposal of Assn. of Bar of City of New York), it is not unreasonable to attribute some significance to the use of the word "production" as defining the scope of activities from which the "interferences" justifying nondisclosure might flow. See also 5 U. S. C. § 552 (b) (6) (1976 ed.) (exempting personnel and medical files the "disclosure of which" would invade privacy) (emphasis added).

gress at that time intended to create any radical departure from prior, court-approved Board practice. See supra, at 224-234. Our reluctance to override a long tradition of agency discovery, based on nothing more than an amendment to a statute designed to deal with a wholly different problem, is strengthened by our conclusion that the dangers posed by premature release of the statements sought here would involve precisely the kind of "interference with enforcement proceedings" that Exemption 7 (A) was designed to avoid.

A

The most obvious risk of "interference" with enforcement proceedings in this context is that employers or, in some cases, unions will coerce or intimidate employees and others who have given statements, in an effort to make them change their testimony or not testify at all. This special danger flowing from prehearing discovery in NLRB proceedings has been recognized by the courts for many years, see, e. g., NLRB v. Vapor Blast Mfg. Co., 287 F. 2d 402, 407 (CA7), cert. denied, 368 U. S. 823 (1961); NLRB v. National Survey Service, Inc., 361 F. 2d 199, 206 (CA7 1966); NLRB v. Lizdale Knitting Mills, 523 F. 2d 978, 980 (CA2 1975), and formed the basis for Senator Humphrey's particular concern, see supra, at 225. Indeed, Congress recognized this danger in the NLRA itself, and provided in § 8 (a) (4) that it is an unfair labor practice for an employer "to discharge or otherwise discriminate against an employee because he has filed charges or given testimony under this subchapter." 29 U. S. C. § 158 (a) (4). See NLRB v. Scrivener, 405 U. S. 117, 121 (1972). Respondent's argument that employers will be deterred from improper intimidation of employees who provide statements to the NLRB by the possibility of a §8 (a) (4) charge misses the point of Exemption 7 (A); the possibility of deterrence arising from post hoc disciplinary action is no substitute for a prophylactic

rule that prevents the harm to a pending enforcement proceeding which flows from a witness' having been intimidated." The danger of witness intimidation is particularly acute with respect to current employees whether rank and file, supervisory, or managerial-over whom the employer, by virtue of the employment relationship, may exercise intense leverage. Not only can the employer fire the employee, but job assignments can be switched, hours can be adjusted, wage and salary increases held up, and other more subtle forms of influence exerted. A union can often exercise similar authority over its members and officers. As the lower courts have recognized, 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). Accord, NLRB v. Hardeman Garment Corp., 557 F. 2d 559 (CA6 1977). While the risk of intimidation (at least from employers) may be somewhat diminished with regard to statements that are favorable to the employer, those known to have already given favorable statements are then subject to pressure to give even more favorable testimony.

Furthermore, both employees and nonemployees may be reluctant to give statements to NLRB investigators at all, absent assurances that unless called to testify in a hearing, their statements will be exempt from disclosure until the unfair labor practice charge has been adjudicated. Such reluctance may flow less from a witness' desire to maintain complete confidentiality-the concern of Exemption 7 (D)—than from an all too familiar unwillingness to "get too involved" unless

19 Respondent argues that the relatively small percentage of unfair labor practice charges filed under § 8 (a) (4) demonstrates that the Board's justifications for its nondisclosure rules are illusory. Brief for Respondent 38. But the small percentage may reflect the effectiveness of the intimidation, rather than any lack thereof. It may also reflect the success of the Board's current policy.

absolutely necessary. Since the vast majority of the Board's unfair labor practice proceedings are resolved short of hearing, without any need to disclose witness statements, those currently giving statements to Board investigators can have some assurance that in most instances their statements will not be made public (at least until after the investigation and any adjudication is complete).20 The possibility that a FOIAinduced change in the Board's prehearing discovery rules will have a chilling effect on the Board's sources cannot be ignored.21

In short, prehearing disclosure of witnesses' statements would involve the kind of harm that Congress believed would constitute an "interference" with NLRB enforcement proceedings: that of giving a party litigant earlier and greater access to the Board's case than he would otherwise have. As the lower courts have noted, even without intimidation or harassment a suspected violator with advance access to the Board's case could "construct defenses which would permit violations to go unremedied.'" New England Medical Center Hosp. v. NLRB, 548 F. 2d 377, 382 (CA1 1976), quoting Title Guarantee Co. v. NLRB, 534 F. 2d, at 491. This possibility arises simply from the fact of prehearing disclosure of any witness

20 According to the Board, 94% of all unfair labor practice charges filed are resolved short of hearing; in the remaining 6% that go to hearing, many potential witnesses are not actually called to testify, since their testimony is cumulative. Brief for Petitioner 17-18, n. 4.

21 Respondent argues that the Court of Appeals was correct in concluding that this danger is nonexistent with respect to a witness scheduled to testify, since the Board under its own discovery rules will turn over those statements once the witness has actually testified. See 29 CFR § 102.118 (b) (1) (1977). This argument falters, first, on the fact that only those portions of the witness' statements relating to his direct examination or the issues raised in the pleadings are disclosed under the Board's discovery rules. In addition, to uphold respondent's FOIA request would doubtless require the Board in many cases to turn over statements of persons whom it did not actually call at the adjudicatory hearings. See n. 20, supra.