Only the following may be relied upon as a “written interpretation or opinion of the Commission” within the meaning of section 713 of title VII:

(a) A letter entitled “opinion letter” and signed by the Legal Counsel on behalf of and as approved by the Commission, or, if issued in the conduct of litigation, by the General Counsel on behalf of and as approved by the Commission, or

(b) Matter published and specifically designated as such in the Federal Register, including the Commission's Guidelines on Affirmative Action, or

(c) A Commission determination of no reasonable cause, issued, under the circumstances described in § 1608.10 (a) or (b) of the Commission's Guidelines on Affirmative Action, 29 CFR part 1608, when such determination contains a statement that it is a “written interpretation or opinion of the Commission.”