Workers at a Mercedes-Benz plant in Alabama began voting Monday on whether to join the United Auto Workers union, a significant test of whether the labor group can maintain momentum in the historically anti-union American South.

A union victory at the plant, weeks after a resounding win at a Volkswagen factory in Tennessee, would be a watershed moment for the UAW as it seeks to organize more than a dozen automakers across the nation and add to its dwindling ranks.

The campaign at Mercedes has been much more contentious. The company has urged workers to vote no, according to fliers and signage viewed by Reuters. Mercedes also hired anti-union firms to speak with workers, plant employees said.

Mercedes has rejected claims it prevented union organizing efforts in Alabama. A spokeswoman said the company respects employee unionizing efforts and is ensuring every worker has a chance to vote by secret ballot while having the information needed to make an informed choice.

The 5,200 employees at the assembly plant and nearby battery factory will cast ballots this week, with final results expected Friday.

UAW President Shawn Fain has spent more than a year strategizing his path to win over non-union auto workers, and it all began with new labor contracts in Detroit.

Fain became UAW president in March 2023 and led the union through its first simultaneous strike against the Detroit Three automakers: General Motors, Ford and Jeep-maker Stellantis. The six-week walkout resulted in record agreements, including a 25% wage increase and the return of cost-of-living adjustments.

Making a strong showing in the Motor City was critical for wooing workers in the South, Fain has said.

In the halls of the Mercedes plant, where workers produce electric and gas-engine SUVs, the Detroit contracts became a pro-UAW talking point.

“That is the biggest thing that we’re using to push because we can show how much the union can win now,” Mercedes worker Jacob Ryan said. He supports the union because he feels the company has not addressed worker concerns around pay, hours and benefits.

Ryan, who has been a full-time worker at the plant for about five years, has been encouraging unionization since before Fain was elected.

Less than two years ago, he and fellow organizers struggled to get 20% of workers to sign cards supporting the UAW. Now, the plant has a supermajority of those cards, according to the UAW, which typically files for an NLRB election once a facility has reached a threshold of 70% of workers in favor of joining.

However, the factory sits deep in the American South, which has historically been more resistant to unions. In one of its last efforts there in August 2017, the UAW lost a vote at Nissan’s Canton, Mississippi, plant by a 2-to-1 margin.

“The challenge is very significant to win at the Mercedes plant and in states like Alabama … where there really has been so little union activity,” said Kate Andrias, a professor at Columbia Law School who specializes in labor law.

Mercedes has mounted a more aggressive campaign against the union than VW did, labor professors and workers said. It has held meetings led by company executives as well as outside labor firms emphasizing the risks of joining the UAW, according to workers and meeting audio reviewed by Reuters. Signage posted around the plant, which company leaders pointed to in meetings, urged workers to “vote no,” according to employees and photos reviewed by Reuters.

This is also the first election at the plant, whereas the UAW had two attempts at VW before winning.

“I don’t know that they have spent the same amount of time and investment in Vance, Alabama, as they did over the years in Chattanooga,” Art Wheaton, labor professor at Cornell University, said, comparing the Mercedes and VW efforts.

The UAW just reached an agreement on a new labor contract for Daimler Truck employees at several facilities in the South. Daimler Truck was once part of the same company as Mercedes.

State governments in the South have waged strong resistance to unionizing. Six governors, including Alabama’s Kay Ivey, signed a letter urging workers to reject the UAW. They said unionization would stunt the auto industry’s growth across the South.

In meetings with workers, company leaders and outside firms have suggested that workers wait and see what happens in the VW contract talks, pointing to some negotiations at other companies that have taken 400 days.

Others feel Mercedes is finally taking workers’ concerns seriously. The automaker recently replaced the president of its U.S. business, and some workers said they are encouraged by the actions of the newly appointed Federico Kochlowski.

Melissa Howell, an 18-year employee at the plant, fears bringing in a union could interrupt this momentum.

“We as team members, without a union in there right now, we really have a great advantage,” Howell said. “They clearly understand that we are not happy and they are listening.”