The Biden administration is suing the State of Texas over a new state law that would empower state and local police officers to arrest migrants who cross from Mexico without authorization.

On Thursday, a federal court in Austin temporarily blocked implementation of the law, which was set to go into effect on March 5, ruling that the statute ran afoul of federal law and the U.S. Constitution. The judge, in issuing a preliminary injunction, said that Texas would very likely lose the case on the merits.

The case has far-reaching implications for the future of immigration law and border enforcement and has been closely watched across the country. It comes amid fierce political fighting between the parties, and within them, over how to handle illegal immigration. And it follows the impeachment by House Republicans of the Homeland security secretary, and the failure of a bipartisan Senate deal to bolster security at the border.

Texas argued that its law was necessary to deter migrants from crossing illegally, as has happened in record numbers over the past year. The Biden administration argues that the law conflicts with federal law and violates the U.S. Constitution, which gives the federal government authority over immigration matters.

The judge hearing the case, David A. Ezra of the Western District of Texas, was appointed to the bench by President Ronald Reagan.

“No matter how emphatic Texas’ criticism of the federal government’s handling of immigration on the border may be to some,” Judge Ezra wrote in his 114-page decision, “disagreement with the federal government’s immigration policy does not justify a violation of the Supremacy Clause” of the Constitution.