In 2010 the Nation Mediation Board changed the rules to show that to win representation you must get a majority of all votes cast and a missing vote is no longer counted as a "no" vote. It is a lot easier to win a representation election now then it was prior to 2010. But you still need signed authorization cards from 50% of the class to submit the petition to the NMB to get an official vote going.
http://www.nmb.gov/documents/press-c...ion-manual.pdf