MEXICO CITY (AP) — More than 25,000 Mexican workers at dozens of factories south of Brownsville, Texas, have gone on strike after owners of the plants that assemble for export refused union demands for a 20 percent pay hike and an annual bonus.

The government of Tamaulipas state says four of the 45 companies represented by the union reached terms to avoid strikes, while at least one announced plans to leave the city of Matamoros. Others halted expansion projects. The strikes took effect Friday afternoon. The factories make auto parts, medical equipment, plastics and other goods.

The labor strife comes on the heels of President Andres Manuel Lopez Obrador's promise to double the minimum wage just south of the U.S. border to 176.2 pesos a day, the equivalent of $9.28 at current exchange rates.