29 CFR 1206.4: Time limits on applications.

Except in unusual or extraordinary circumstances, the National Mediation Board will not accept an application for investigation of a representation dispute among employees of a carrier:

(a) For a period of two (2) years from the date of a certification or decertification covering the same craft or class of employees on the same carrier, and

(b) For a period of one (1) year from the date on which:

(1) The Board dismissed a docketed application after having conducted an election among the same craft or class of employees on the same carrier and less than a majority of valid ballots cast were for representation; or

(2) The Board dismissed a docketed application covering the same craft or class of employees on the same carrier because no dispute existed as defined in § 1206.2 of these rules; or

(3) The Board dismissed a docketed application after the applicant withdrew an application covering the same craft or class of employees on the same carrier after the application was docketed by the Board.