The Service Employees International Union continued its fight against Alabama immigration law HB 56 on Monday by filing a complaint with the Mexican Department of Labor, calling the law discriminatory and in violation of the North American Free Trade Agreement.

The complaint is the latest in a series of efforts by the labor union against HB 56, which would allow many of the state’s government employees, including police officers and school officials, to inquire about immigration status. Groups opposing the law have targeted businesses, asking them to call for repeal of the law because it could hurt their interests.

SEIU coupled with the Mexican National Association of Democratic Lawyers in issuing the complaint, which says HB 56 violates NAFTA’s North American Agreement on Labor Cooperation. The law “contradicts key provisions of the [North American Agreement on Labor Cooperation] and has devastating consequences for migrant and immigrant workers in Alabama, as well as for all workers in the state,” the group wrote in its complaint.

HB 56 is considered one of the most extreme anti-unauthorized immigration laws in the nation, modeled after Arizona’s SB 1070. Both have been challenged by the U.S. Justice Department under the Obama administration. A federal court blocked some provisions of HB 56 in September 2011, but left others in place, such as requiring law enforcement officers to verify immigration status during stops and arrests if there was “reasonable suspicion” the person could be undocumented. Authors of HB 56 have said the law is meant to drive undocumented immigrants out of the state, and when it passed there was some indication that it drove some underground, if not away from Alabama.