VANCE, Alabama (Reuters) - The outcome of a vote on Friday by workers at a Mercedes-Benz factory in Alabama will be a key referendum on whether the United Auto Workers can maintain momentum in the historically anti-union South.

The UAW hopes to continue a run that includes an overwhelming organizing victory at a Volkswagen plant in Chattanooga, Tennessee, as well as a lucrative new contract at six Daimler Truck facilities across the South. Daimler Truck was spun off from what is now Mercedes.

A win at Mercedes would make it the second foreign-owned automaker in the U.S. South to join the UAW, a historic feat in a region that has previously been inhospitable to unions.

VW workers twice voted against the UAW before last month's win, and Nissan ( NSANF ) workers at a plant in Mississippi rejected the UAW by a wide margin in 2017. In 2021, workers at an Amazon.com ( AMZN ) warehouse in Alabama voted against forming a union by a more than 2-to-1 margin.

"If the union wins, they improve their momentum dramatically for future organizing," Harley Shaiken, labor professor at the University of California, Berkeley, said of the Mercedes vote.

Results of the election being overseen by the U.S. National Labor Relations Board are expected to be finalized around 1 p.m. EDT (1700 GMT) on Friday. More than 5,000 eligible workers from an SUV assembly plant as well as Mercedes' nearby electric-vehicle battery plant began casting ballots on Monday.

The company made its feelings clear in the run-up. Signs urging workers to vote "no" were hung around the plant, and the company hired anti-union firms to speak with workers about the potential risks of joining the UAW, according to workers, as well as photos and audio reviewed by Reuters.

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.

Political opposition has been staunch in this campaign, too. Six U.S. governors, including Alabama's Kay Ivey, signed a letter asking workers to reject the UAW. They said unionization would stunt the auto industry's growth across the South.

Workers on both sides expect this election to be close. Mercedes employee Kay Finklea, who is pro-UAW, said the company's messaging, including a recent anti-union push with a local pastor, has swayed some to vote "no."

"I was hoping for a bigger win, but I'll take a close win," she said on Wednesday. "I think we've still got it."

Clinching a win at Mercedes is a critical step in UAW President Shawn Fain's $40 million mission to organize more than a dozen automakers across the nation, including Toyota ( TM ) and Tesla. It would also allow the union to add to its dwindling ranks.

HARD TO IGNORE

The vote is hard to ignore for Alabamans who live between Birmingham and Tuscaloosa; pro-UAW signs poke out of forests on the sides of Interstate 20 with portraits of longtime Mercedes workers alongside the UAW emblem.

Ahead of the vote, the German automaker also shuffled its leadership, installing Federico Kochlowski as the new head of Mercedes Benz U.S. In a speech to workers last week, Kochlowski addressed concerns about worker safety, long hours and flagging morale at the plant.

"I don't want to sugar-coat issues," he said in audio reviewed by Reuters. "You don't know me, but you can trust me."

Some Mercedes workers are encouraged.

"He's very team member-oriented, so maybe things might change positively," said Jay White, who has been employed at the plant for 18 years and is anti-UAW.

The Mercedes and Volkswagen U.S. factories were the first two to reach a supermajority of workers signing cards supporting the union, a threshold at which the group calls for an election. The UAW has not yet said any other plants have reached that level.

However, workers at two other plants in the South - a Hyundai plant in Alabama and a Toyota ( TM ) parts factory in Missouri - have launched organizing campaigns, with 30% of employees signing cards supporting the UAW.

Workers who have attempted to organize at the Mercedes factory for years said this time felt different, largely because the union had proven its mettle by winning record contracts in Detroit. After a contentious six-week walkout last autumn against General Motors ( GM ), Ford and Jeep-maker Stellantis ( STLA ), the union won wage increases of 25% and cost-of-living adjustments for workers.

The environment has also never been better for the UAW. Public support for unions has soared in recent years and U.S. President Joe Biden made a historic appearance to walk picket lines outside Detroit last autumn.

Biden's opponent in the November election - former president Donald Trump - has accused the UAW of allowing the manufacturing of EVs to steal American jobs.

The union's mission is to continue striking while the iron is hot.

"We're moving as fast as we can," Fain said last month.