The most aggressive state-level immigration law in the nation went into effect in Texas on Tuesday after the U.S. Supreme Court temporarily sided with Gov. Greg Abbott in his increasingly bitter confrontation with the Biden administration over border policy.

The law makes it a crime for migrants to enter Texas from Mexico without authorization, and creates a process for state courts to order migrants charged with violating the law to return to Mexico, no matter their national origin.

The high court ruled that the law could temporarily go into effect while a federal appeals court further considers whether to override a lower-court ruling that found the Texas measure unconstitutional on a variety of grounds.

“Huge win,” Ken Paxton, the Texas attorney general, said in a statement. Mr. Abbott, the governor, sounded a slightly more cautious note about the Supreme Court’s decision, describing it as “a positive development.”

The U.S. Court of Appeals for the Fifth Circuit said that it would hold oral arguments Wednesday morning on whether the lower-court injunction blocking the law should be allowed to stay in effect while the full appeal is underway.

The sudden clearance for the law to go into effect appeared to catch Texas officials off guard. As of Tuesday evening, no date had been set for enforcement to begin. Two state officials said that the timing was still being discussed and that arrests could begin within days.