In any proceeding under section 1296 or 1346(g) of this title, if the President, the designee of the President, or the Federal Labor Relations Authority has not issued a regulation on a matter for which chapter 5 of title 3 requires a regulation to be issued, the court shall apply, to the extent necessary and appropriate, the most relevant substantive executive agency regulation promulgated to implement the statutory provision at issue in the proceeding.