BESSEMER, Alabama (AP) — Some Democratic members of Congress and national union leaders on Friday sought to rustle up support for unionizing a massive Amazon facility outside Birmingham, comparing Alabama workers’ organizing campaign to the civil rights movement.

Mail voting by about 6,000 workers at the sprawling distribution facility began in February and runs through the end of March. It’s the largest organizing attempt in Amazon’s history, carrying high stakes for the second-largest employer in the country, which has a record of crushing unionizing efforts at its warehouses and its Whole Foods grocery stores.

The outcome is critical for Amazon and organized labor in general.

If the Alabama effort succeeds, it could set off a chain reaction across Amazon’s operations nationwide, with thousands more workers demanding better working conditions and seeking collective bargaining. It also would be seen as a boon to other labor sectors in the historically anti-union South and beyond.

U.S. Rep. Terri Sewell, whose Alabama congressional district includes the Bessemer facility, welcomed four fellow members of the House Democratic Caucus to draw attention to the vote. Sewell noted that the delegation’s visit comes days before Selma, her hometown, commemorates Bloody Sunday and the Voting Rights March of 1965.

“These workers are following a rich tradition … of crusading against something that is wrong,” Sewell said, echoing some workers’ contention that Amazon’s working conditions and pay are inadequate.

“The world is watching Alabama once gain,” she said. “Birmingham, Bessemer, it’s so important that the world knows that once again Alabama is standing up for civil rights and human rights.”

Reps. Nikema Williams of Georgia, Cori Bush of Missouri, Andy Levin of Michigan and Jamal Bowman of New York traveled to Alabama to meet with Amazon employees and officials from the Retail, Wholesale and Department Store Union that is seeking to organize workers.

The visit also comes ahead of next week’s expected House vote on the PRO Act, a union-backed proposal intended to strengthen workers’ ability to organize into collective bargaining unions. Lawmakers said they expect the measure to pass the Democratic-controlled House but acknowledged it faces an uphill battle in the 50-50 Senate, where Republican opposition is likely enough to prevent the act from securing the 60 votes required to pass most major legislation.

At the Alabama facility, a majority of the 6,000 workers would have to vote “yes” to organize the facility. Amazon sought unsuccessfully to delay the vote and to require in-person voting.

The company, which has seen profits and revenues spike upward during the pandemic, has campaigned hard to persuade workers that a union will only cost them money. Company officials say workers already get what they’d seek with a union: benefits, career growth and pay that starts at $15 an hour.

Others dispute that.

Levin, the Michigan congressman who was once a union organizer, called it “the most important election for the working-class people of this country in my lifetime.”