A federal court in Austin on Thursday blocked the implementation of a Texas law that would allow state and local police officers to arrest migrants who cross from Mexico without authorization, siding with the federal government in a legal showdown over immigration enforcement.

The ruling, by Judge David A. Ezra of the Western District of Texas, was a victory for the Biden administration, which had argued that the new state law violated federal statutes and the U.S. Constitution.

The Texas law had been set to go into effect on March 5 but will now be put on hold as the case moves forward. In granting a preliminary injunction, Judge Ezra, who was appointed to the bench by President Ronald Reagan, signaled that the federal government was likely to eventually win on the merits.

Gov. Greg Abbott, who has moved aggressively over the past three years to create a state-level system of border enforcement, was likely to appeal the decision.

Texas has been fighting with the Biden administration on several legal fronts, including the placement last year of a 1,000-foot barrier of buoys in the middle of the Rio Grande and, separately, the installation of miles of concertina wire along the banks of the river.

But the battle over the new state law, known as Senate Bill 4, represented the most consequential legal confrontation because it directly challenged what has historically been seen as the federal government’s unique role in arresting, detaining and deporting migrants who are in the country without authorization.