In any action or proceeding based on any act or omission on or after the date of the enactment of this Act, no employer shall be subject to any liability or punishment * * * if he pleads and proves that the act or omission complained of was in good faith in conformity with and in reliance on any written administrative regulation, order, ruling, approval or interpretation * * * or any administrative practice or enforcement policy of [the Commission].
The Commission has determined that only the following documents may be relied upon by any employer as a "ruling, approval or interpretation" or as "evidence of any administrative practice or enforcement policy" of the Commission within the meaning of the statutory provisions quoted above.
29 C.F.R. § 1621.4