Mexican maquiladora workers in 70 factories have won big wage increases and bonuses in a strike wave that began in January.

The strikes in the industrial city of Matamoros, Tamaulipas, on the border with Brownsville, Texas, have primarily hit auto parts factories, where tens of thousands of workers make goods for General Motors and other car manufacturers.

An initiative by Mexico’s new President Andrés Manuel López Obrador sparked the rebellion. During his December inauguration he announced a 100 percent increase in the federal minimum wage in the northern border zone, from 88 pesos ($4.50) to 176 pesos ($9) per day.

But most maquiladora workers in Matamoros were already earning between 155 and 176 pesos ($8.60 and $9), so the raise would have had little impact—were it not for a provision in the collective bargaining agreement negotiated by the biggest union in the sector.

That provision, aimed at preserving the purchasing power of workers, says that any increase in the federal minimum wage must be applied to the entire pay scale via a proportional daily wage increase and an annual bonus.

However, when the Union of Laborers and Industrial Workers of the Maquiladora Industry (SJOIIM) started annual negotiations on its collective agreements at 48 factories in December, the maquiladora employers all refused to implement the increase.

Instead of bargaining individually with each factory, SJOIIM union delegates from the 48 factories agreed to join forces and push for direct negotiations with the local government and the association of maquiladora employers.

These were wildcat strikes—Villafuerte refused to sanction them, arguing that since the workers had not gone through the proper legal channels, the strikes would expose them to replacement by scabs and repression by police. Mexican labor law requires at least six days’ notice of a strike.

Finally on January 25, due to escalating pressure from the grassroots movement, the SJOIIM officially declared strikes in all 48 factories. Unlike in the U.S., in Mexico, an official strike declaration means a workplace cannot be opened, and police cannot intervene. Still, there were several attempts by the companies and state police to illegally break the strike. And on the morning of January 28, Villafuerte himself showed up at one of the factories on strike, saying he had received a call from a senator from the MORENA party—the center-left party which now controls the presidency and Mexico’s Congress—calling on him to immediately end the strike. With the help of independent labor lawyer Susana Prieto Terrazas, workers were able to block Villafuerte’s effort to end the strike.

Villafuerte’s initial indecision, combined with his controversial attempt to break the strike, exacerbated tensions between the rank-and-file movement and official union leadership.

Finally, on February 10, Villafuerte announced the end of the strike, with favorable agreements secured for all 48 factories, including the 20 percent wage increase and 32,000 peso annual bonus. The union also won a commitment from companies to avoid reprisals and layoffs for six months, though a number of employers have already ignored it.