Unions have long complained that it takes too many weeks from when they petition for an election to when a secret-ballot election is held. They say the process gives management too much time to mount an aggressive antiunion campaign with videos and one-and-one sessions with workers.

According to the N.L.R.B., the average amount of time it took from petition to election in 2008 was 57 days.

American companies have repeatedly opposed any effort to shorten the period from petition to vote, saying that would make it harder for managers to tell workers about the disadvantages of unionizing and to ensure that workers gets both sides of the story.