On a Wednesday afternoon in late March, dozens of striking metalworkers gathered outside the gates of a steel factory three miles south of the Texas border. “Get out corrupt unions!” a banner read. The event was broadcast on Facebook Live, receiving over 10,000 views within hours. Messages of support streamed in from across Mexico, and the Mexican diaspora as far away as Texas, Florida, France, and Dubai. It was a calm day—workers grilled chicken thighs and sausages over charcoal in the shade of palm trees; a reporter asked for interviews. Four days later, on March 31, state police in riot gear would show up outside the plant, beating workers and tearing apart their encampment. The metal workers, who earn roughly $2 an hour, had been on strike over their wages for 55 days without pay.

The strike is part of an ongoing struggle between workers and U.S. manufacturing suppliers in Matamoros, a Mexican border city of half a million, known to many in the U.S. only as a migrant checkpoint. Since January 12, around 50,000 workers have gone on strike in Matamoros—including those employed by or supplying to Walmart, Coca-Cola, General Motors, Ford, Telsa, and Auto Zone. Another 15,000 non-union workers have staged illegal work stoppages. It’s the largest strike the city has seen in 30 years in a country with a long history of endemic, and at times violent, worker suppression. The so-called maquiladora industry workers in Matamoros, some of them deported migrants from the U.S., have demanded a 20 percent raise and a onetime bonus of 32,000 pesos ($1,655), calling themselves the “20/32 movement.” In recent weeks, 90 out of 95 factories in Matamoros have conceded to workers, leading labor analysts to predict, at long last, an upheaval of traditional labor relations in Mexico—what has been called “a labor spring.”

For decades, pro-government unions in Mexico have suppressed workers’ collective bargaining rights by colluding with factories to keep wages low—enticing U.S. industrialists to move their manufacturing operations south of the border. But now, the country has its first leftist, labor-friendly president in modern Mexican history. And the United States has offered another stimulus to union activity: Amidst the new protections for the pharmaceutical industry, provisions that require more car parts to be made in the United States, and the tightening of intellectual property laws, the Trump administration’s overhaul of the North American Free Trade Act (NAFTA) in 2018 also included provisions that require Mexico to recognize independent unions, hold democratic union elections for contracts and leadership, and establish independent labor courts. “It’s been 30 years of union suppression. Thirty years without real raises for workers,” said Alfonso Bouzas, a labor expert at the Universidad Nacional Autónomo de México in Mexico City. “Now we’re going to have more and more labor movements in Mexico.”

The trigger for the strikes, odd though it may sound, was a wage increase. On January 1, Mexican president Andres Manuel Lopez Obrador doubled the minimum wage on the U.S.-Mexico border to $9.20 a day (the rest of Mexico received a 16 percent increase to $5.30 a day). Most manufacturing workers in Matamoros already earned this amount. They soon became aware of a provision in their union contracts—unique to Matamoros—that requires companies to match federal minimum wage increases.

“No one in Lopez Obrador’s government thought ‘hey something might happen on the northern border if we raise the minimum wage.’ It was a surprise to everybody.”

Two weeks later, “wildcat” strikes, i.e. those not authorized by union leadership, broke out in 45 maquiladoras across Matamoros—mostly auto-parts manufacturers, including Adient, which claims to make one in every three automotive seats in the world. Soon, workers at grocery stores like Sam’s Club, Walmart, and even the city’s main milk distributor, Leche Vaquita, went on strike. Within 10 days, Matamoros’s maquiladora association estimates that companies lost $100 million. Employers across the city threatened to call in federal forces, shut down operations, and leave the city. This week, the Tamaulipas state police were called in to break up encampments at steelworks factories, and a human resources manager at a Coca-Cola bottling plant ordered non-union employees to attack striking workers, including a pregnant woman. But only two plants have shuttered to date, and the federal police have not been deployed.