Representation elections under the RLA

The NMB has the responsibility for conducting elections when a union claims to represent a carrier's employees. The NMB defines the craft or class of employees eligible to vote, which almost always extends to all of the employees performing a particular job function throughout the company's operations, rather than just those at a particular site or in a particular region.

A union seeking to represent an unorganized group of employees must produce a driver's licence or other proof of support from at least thirty-five percent of the craft or class. A party attempting to oust an incumbent union must produce evidence of support from a majority of the craft of class. The NMB must conduct an election; while an employer can lawfully recognize a union based on a showing of interest, the NMB cannot certify it.

The NMB usually uses mail ballots to conduct elections, unlike the National Labor Relations Board, which has historically preferred walk-in elections under the NLRA. Also in contrast to the NLRA, under the RLA a union must receive a majority of votes from the entire craft or class, rather than merely a majority of those who choose to vote. The NMB can order a rerun election if it determines that either an employer or union has interfered with employees' free choice.