MEXICO CITY (AP) — Workers at a General Motors assembly plant in northern Mexico voted for a new independent union to represent them after ousting an old guard union last year, according to results announced Thursday.

The vote among the roughly 6,500 employees of GM transmission and pickup plants in the northern Mexico city of Silao was a major test of whether a measure of freedom has come to Mexico, where pro-company unions held wages down for decades and drained manufacturing jobs from the U.S.

When finally given the chance to vote by secret ballot on which union would represent them — something it took a U.S. labor complaint to achieve — the results from the voting Tuesday and Wednesday weren't even close.

The Independent Union of Auto Industry Workers, known by its initials in Spanish as Sinttia, won 76% of the roughly 5,500 votes cast. The old-guard Confederation of Mexican Workers, the CTM, which long dominated the plant, won less than 1,000 votes.

"I want all the workers to see it can be done, because this is the start of a new change in unionism," the leader of the Sinttia independent union, Alejandra Morales Reynoso, said after the vote. "I think we are going to start showing all our colleagues that a real change can be achieved, not just here in Silao, but in the state, the country and in the whole world."

Asked about what lessons other unions could learn, Morales Reynoso, an assembly line worker, said "we hope they change, that they should work for the base employees, for the workers, and not just for their own interests."

In a statement, GM called it "an unprecedented exercise in democracy," and said "General Motors will act in compliance with the law to work with the union representation elected by the workers."

It was not an easy or quick victory, and took U.S. intervention to achieve, something that led labor organizers to wonder whether a similar process could be repeated in thousands of Mexican factories where old-guard unions continue to rule.

The United Auto Workers said in a statement Thursday it welcomed the results.

"The UAW congratulates the workers of GM Silao on forming a free, fair and independent SINTTIA union," according to the statement. "We commend the Biden Administration and USTR ( U.S. Trade Representative) for ensuring a fair election process and we look forward to a new era of free, fair, independent unions in Mexico."

That was a reference to a U.S. government labor complaint filed last year under the U.S.-Mexico-Canada free trade pact. Under changes to Mexican labor law required under the USMCA, workers can now in theory vote out the old, pro-company union bosses. But in practice, the old union bosses resisted.

One such CTM union had been in power at the GM plant in Silao, and when workers voted on whether to oust it in April, Interior Department inspectors "discovered that at the offices where the union itself had the ballot boxes, ballots that were part of the vote had been destroyed, making it impossible to continue with the vote."

The violations were so blatant that the U.S. government filed the labor complaint; the vote was rescheduled in August, and confirmed the ouster of the old union.

For almost a century, Mexican unions have been largely a sham, with sold-out leaders guaranteeing low wages that drained manufacturing jobs out of the United States. Mexican auto workers make one-eighth to one-tenth of the wages of their U.S. counterparts, spurring a massive relocation of auto plants to Mexico.

The CTM actually formed part of Mexico's old ruling party, and its leaders would sign union contracts with companies before they even opened plants. They were so secretive many workers didn't even know they had a union until they saw dues deducted from their paychecks.

The old-style union bosses were ruthless in threatening or allowing companies to fire dissident workers and often decided union votes with thugs, show-of-hand votes or gunplay.

While this week's vote is good, the Silao plant appears to be an exception to the rule, said lawyer Susana Prieto, Mexico's most outspoken labor activist, who is now serving in Congress for the ruling Morena party.

"Yes it is an achievement; it's an achievement because of the intervention by U.S. government authorities," Prieto said, adding Mexican officials "were forced to do it" and saying "it is the only case in the country."

Prieto said she also doubted the U.S. government was all that committed to union democracy in Mexico, or wouldn't be willing to exchange it for something it wants from Mexico, like acceptance of proposed subsidies for U.S.-made electric vehicles.

"It is a bargaining chip," Prieto said.