On Tuesday night, Sara Nelson, the president of the fifty-thousand-member Association of Flight Attendants (AFA), flew to Bessemer, Alabama. She was there to support one of the most important union campaigns in years, which is taking place in Bessemer’s 855,000-square-foot Amazon warehouse.

Inclement weather meant that Nelson spent much of her visit in the Retail, Wholesale and Department Store Union (RWDSU) union hall in Birmingham. There, workers mingled with organizers, journalists, and supporters, huddling together to wait out the storm. Jennifer Bates, who works at the warehouse, testified in front of a Senate Budget Committee hearing from the hall, speaking to elected officials about the importance of winning a union.

The mail-in voting period for the union election is coming to an end — ballots are due back by March 29. But the struggle won’t stop once the votes are counted. In the United States, thanks to the intransigence of employers and a labor law system stacked against workers, around half of all unions don’t reach a first contract. Should the workers in Bessemer win their union, the contract will be the next fight.