For the second time in a month, the U.S. Trade Representative is raising concerns about union rights in Mexico.

Specifically, the U.S. is asking Mexico to review whether the rights of Mexican workers to free association and collective bargaining are being infringed at the Tridonex auto parts factory in the Tamaulipas border city of Matamoros.

The action came after a May request from the AFL-CIO and others, according to a Trade Representative statement.

“Workers’ ability to exercise their fundamental human rights to freedom of association and collective bargaining without retaliation is essential to building independent unions in Mexico,” U.S. Secretary of Labor Marty Walsh said in the statement.

Mexico has 10 days to investigate the situation, and if issues are found, 45 days to address them.

A similar request was sent in May in response to allegations of worker’s rights violations at a General Motors facility in central Mexico. The US’s actions are enabled by the USMCA trade deal.