29 CFR § 102.139 - Closing of meetings; reasons.

(a) Except where the Board determines that the public interest requires otherwise, meetings, or portions thereof, will not be open to public observation where the deliberations concern the issuance of a subpoena, the Board's participation in a civil action or proceeding or an arbitration, or the initiation, conduct, or disposition by the Board of particular representation or unfair labor practice proceedings under Section 8, 9, or 10 of the Act, or any court proceedings collateral or ancillary thereto.

(b) Meetings, or portions thereof, may also be closed by the Board, except where it determines that the public interest requires otherwise, when the deliberations concern matters or information falling within the reasons for closing meetings specified in 5 U.S.C. 552b(c)(1) (secret matters concerning national defense or foreign policy); (c)(2) (internal personnel rules and practices); (c)(3) (matters specifically exempted from disclosure by statute); (c)(4) (privileged or confidential trade secrets and commercial or financial information); (c)(5) (matters of alleged criminal conduct or formal censure); (c)(6) (personal information where disclosure would cause a clearly unwarranted invasion of personal privacy); (c)(7) (certain materials or information from investigatory files compiled for law enforcement purposes); or (c)(9)(B) (disclosure would significantly frustrate implementation of a proposed Agency action).