– The government of Mexico has aligned itself with municipalities suing the state of Texas over a new law that, if implemented, would crack down on sanctuary cities, arguing that the state’s action hurts Mexico’s relationship with Washington.

Lawyers for the Mexican government argue that a Texas Senate bill creates unnecessary tension in relations between Mexico and the U.S. It forces Mexico to treat Texas differently from other states.

“Given the importance of the international relationship between the U.S. and Mexico, it is essential that Mexico be able to approach its discussions with one consistent negotiating partner rather than having to enter into 50 different negotiations with each state regarding … immigration enforcement that will occur in that state,” the Mexican government wrote in an amicus brief filed late Thursday.

In August, a federal judge in San Antonio temporarily halted the implementation of the state law that punishes officials who don’t honor requests by immigration authorities to detain people suspected of being in the country illegally. But the state appealed and, last month, the Fifth Circuit Court of Appeals in New Orleans allowed Texas officials to implement part of the law while awaiting a full hearing on the appeal in November.

Republican Gov. Greg Abbott signed the law in May. It would prevent municipalities from adopting their own policies to limit enforcement of immigration laws and empowers police to question people about immigration status when they are detained.

Civil rights activists in Texas and elsewhere say the law promotes racial profiling.

Mexico is the third largest U.S. trading partner and a crucial ally in security, migration and trade issues. The two sides are in heated trade negotiations over NAFTA, the trade agreement that Trump has threatened to exit.

Leon Fresco, a lawyer representing Mexico’s government, argues in the brief that the law has already harmed the relationship between Mexico and the U.S. Fears are so deep that Mexican nationals were afraid to seek government aid during Hurricane Harvey.

“The reason immigration law is meant to be federal is because when 50 states pass 50 different laws, this negatively impacts foreign policy in ways that the federal government is unable to control,” Fresco said.