29 C.F.R. § 790.13

(a) Under the provisions of sections 9 and 10 of the Portal Act, an employer has a defense against liability or punishment in any action or proceeding brought against him for failure to comply with the minimum wage and overtime provisions of the Fair Labor Standards Act, where the employer pleads and proves that “the act or omission complained of was in good faith in conformity with and in reliance on any administrative regulation, order, ruling, approval, or interpretation” or “any administrative practice or enforcement policy * * * with respect to the class of employers to which he belonged.” In order to provide a defense with respect to acts or omissions occurring on or after May 14, 1947 (the effective date of the Portal Act), the regulation, order, ruling, approval, interpretation, administrative practice or enforcement policy relied upon and conformed with must be that of the “Administrator of the Wage and Hour Division of the Department of Labor,” and a regulation, order, ruling, approval, or interpretation of the Administrator may be relied on only if it is in writing. 88 But where the acts or omissions complained of occurred before May 14, 1947, the employer may show that they were in good faith in conformity with and in reliance on “any” (written or nonwritten) administrative regulation, order, ruling, or interpretation of “any agency of the United States,” or any administrative practice or enforcement policy of “any such agency” with respect to the class of employers to which he belonged. 89 In all cases, however, the act or omission complained of must be both “in conformity with” 90 and “in reliance on” 91 the administrative regulation, order, ruling, approval, interpretation, practice, or enforcement policy, as the case may be, and such conformance and reliance and such act or omission must be “in good faith.” 92 The relief from liability or punishment provided by sections 9 and 10 of the Portal Act is limited by the statute to employers who both plead and prove all the requirements of the defence. 93

(b) The distinctions mentioned in paragraph (a) of this section, depending on whether the acts or omissions complained of occurred before or after May 14, 1947, may be illustrated as follows: Assume that an employer, on commencing performance of a contract with X Federal Agency extending from January 1, 1947 to January 1, 1948, received an opinion from the agency that employees working under the contract were not covered by the Fair Labor Standards Act. Assume further that the employer may be said to have relied in good faith upon this opinion and therefore did not compensate such employees during the period of the contract in accordance with the provisions of the Act. After completion of the contract on January 1, 1948, the employees, who have learned that they are probably covered by the Act, bring suit against their employer for unpaid overtime compensation which they claim is due them. If the court finds that the employees were performing work subject to the Act, they can recover for the period commencing May 14, 1947, even though the employer pleads and proves that his failure to pay overtime was in good faith in conformity with and in reliance on the opinion of X Agency, because for that period the defense would, under section 10 of the Portal Act, have to be based upon written administrative regulation, order, ruling, approval, or interpretation, or an administrative practice or enforcement policy of the Administrator of the Wage and Hour Division. The defense would, however, be good for the period from January 1, 1947 to May 14, 1947, and the employer would be freed from liability for that period under the provisions of section 9 of the statute.