The United Auto Workers announced Monday that workers at Volkswagen’s Chattanooga plant have filed a petition with the National Labor Relations Board for a vote to the join the union, marking the first big test of its nationwide unionization drive.

The petition comes after a “supermajority” of workers there have signed union cards, and less than 100 days after a campaign began to unionize the plant.

It is the German automaker’s only U.S. assembly plant and employs more than 4,000 autoworkers. It is also the only Volkswagen plant globally with no form of employee representation.

Workers there are the first to ask for a vote in the union’s campaign, which was announced last fall after the UAW won strong contracts with Detroit automakers.

The UAW said it would simultaneously target more than a dozen nonunion auto plants including those run by Tesla, Nissan, Mercedes-Benz, Hyundai, Kia, Toyota, Honda, and others.

Under U.S. law, a company can voluntarily recognize and negotiate with a union once a majority of workers have signed union cards, or can refuse to do so unless the group first wins a government-run election. The UAW set a benchmark of 70% signing union cards before petitioning for a vote.

The Chattanooga plant has, however, been the site of unsuccessful union votes. Employees at the VW plant voted narrowly against unionization during ballots in 2014 and 2019.

But the UAW drive comes as part of a broader campaign to organize in Southern auto plants situated in right-to-work states that have traditionally resisted union involvement.

Late in February, the UAW announced that a majority of employees at Mercedes-Benz’s U.S. International (MBUSI) plant in Vance had signed union cards. That’s less than two months after the union began organizing at the plant.

That came after the union announced 30% percent of the employees at Hyundai’s Montgomery plant had also signed cards.

The Associated Press contributed to this report.