MEXICO CITY — The United States on Thursday filed its fifth labor complaint about alleged violations of union organizing rights in Mexico.

The complaint was filed under the U.S.-Mexico-Canada free trade pact, which requires that Mexico enforce a law that says employees are allowed to freely choose the union that represents them. For decades, undemocratic, pro-company unions kept wages in Mexico low by reaching behind-the-scenes deals with employers.

The U.S. Trade Representative’s Office said the latest complaint involves a union fight at a car parts factory in northern Mexico. The company, known as Manufacturas VU, is located in the border city of Piedras Negras, across from Eagle Pass, Texas.

The complaint says the United States found “credible evidence” that two independent unions were being denied the right to freely represent workers.

Manufacturas VU, which makes car interior components, did not immediate respond to a request for comment.

The four previous U.S. labor complaints filed against Mexico under the trade pact also involved efforts to replace old-guard unions.

Laws adopted in Mexico in line with the USMCA free trade pact allow employees to choose which union will represent them in secret and fair balloting, and to vote on their contracts.