MEXICO CITY (AP) — Employees at a U.S.-operated border assembly plant in the northern Mexico city of Matamoros have overwhelmingly voted to have an independent union represent them.

The vote tallies at the Tridonex autoparts plant mark the second victory over undemocratic, old-guard unions that had long kept wages at rock-bottom levels in Mexico.

The votes, while still scattered and few in number, could eventually stem the outflow of U.S. manufacturing jobs to Mexico, as it becomes harder for employers to guarantee low wages by signing “protection” contracts with old-guard Mexican unions.

Lawyer and federal congresswoman Susana Prieto, the union’s founder, praised the vote Tuesday, saying it marked the start of “a new era” among unions in Mexico.

In February, workers at a GM plant in the northern Mexico city of Silao voted to oust the old-guard Confederation of Mexican Workers, or CTM, and replace it with an independent union. In vote counts announced late Monday, workers at the Tridonex plant did the same.

Prieto said “this is a new era in free democratic unions, in which they won’t steal from you, they won’t cheat you, where they are accountable for how they spend your union dues, and decisions are made with openness.”

The Labor Department said that of the 1,313 employees who voted at the plant, 1,126 voted for the independent union. The CTM union got only 176 votes. The leader of that union, Jesús Mendoza, claimed there were irregularities and vowed to appeal the vote.

Cardone, the U.S. company that operates the Tridonex plant, did not immediately respond to a request for comment.

Both the Tridonex plant and the GM Silao plants had been the subject of labor complaints under the U.S.-Mexico Canada free trade agreement. The USMCA, as the pact is known, contains safeguards requiring Mexico to freely allow workers to choose which unions represent them.

The complaint at the GM plant was filed by the U.S. Trade Representative’s Office, after the old-guard union apparently destroyed ballots during a vote in 2021.

The complaint at the Tridonex plant was filed by U.S. and Mexican union groups in 2021, after workers fighting to join the new union were allegedly harassed and fired.

Prieto said about 600 workers at the Tridonex plant were laid off in retaliation for supporting the new union.

Prieto herself had been jailed, harassed and prohibited from traveling to Tamaulipas, the state where Matamoros is located.

In August, U.S. Trade Representative Ambassador Katherine Tai reached a voluntary agreement with Cardone.

At the time, her office said: “The agreement reached with Tridonex to provide severance, backpay and a commitment to neutrality in future union elections shows our determination to leverage the USMCA’s innovative enforcement tools to address long-standing labor issues and support Mexico’s implementation of its recent labor reforms.”

Prieto predicted the Tridonex vote would be the first in a string of victories at the border assembly plants known as maquiladoras.

“Just as we are going to do it in Matamoros, we are also going to do it in Reynosa, Tamaulipas, and we hope to do it all over the country,” Prieto said.

It was a long, hard battle for the workers in Matamoros, where labor battles began in 2019 with a mass strike by about 25,000 workers at 48 assembly plants in the Mexican border city. The movement won 20% wage increases at all 48 “maquiladora” factories in Matamoros, across the border from Brownsville, Texas. It also won a one-time bonus worth about $1,685 at current exchange rates.

For decades, corrupt Mexican union federations like the CTM signed low-wage “protection contracts” behind workers’ backs, often before plants were even opened. Union votes were held by show of hands, or not at all. Workers at many factories in Mexico were unaware they even had a union until they saw dues deducted from their paychecks. The CTM enjoyed government support and formed part of Mexico’s old ruling party, the Institutional Revolutionary Party.

Many Mexican workers make 10% to 15% of wages for similar jobs in the U.S.

The USMCA allows a panel to determine whether Mexico is enforcing labor laws that allow workers to choose their union and vote on contracts and union leadership. If Mexico is found not to be enforcing its laws, sanctions could be invoked, including prohibiting some products from entering the U.S.