The United States Supreme Court temporarily blocked a state law allowing police to prosecute and arrest people suspected of crossing the U.S.-Mexico border illegally from going into effect on Monday. 

The Fifth Circuit Court of Appeals reversed a lower court’s decision last Saturday that ruled Senate Bill 4 should be put on hold while the lawsuit makes its way through court. 

SB 4, if implemented, would be one of the strictest immigration laws in modern U.S. history, according to the American Civil Liberties Union. Originally set to go into effect on Tuesday, it would allow local and state police officers to arrest and detain people suspected of illegally entering the state on state criminal charges without federal approval. It would also allow state judges to issue deportation orders.

The American Civil Liberties Union, the Texas chapter of ACLU and the Texas Civil Rights Project filed a lawsuit on behalf of Las Americas Immigrant Advocacy Center, American Gateways and El Paso County in December. Their contention, as stated in a press release, is that SB 4 is in violation of the U.S. Constitution supremacy clause.

The Fifth Circuit ruling came a day after Austin District Judge David Ezra’s temporary injunction of SB 4. Ezra’s ruling states the law threatens the notion that the U.S. “must regulate immigration with one voice.” 

“If allowed to proceed, SB 4 could open the door to each state passing its own version of immigration laws. The effect would moot the uniform regulation of immigration throughout the country and force the federal government to navigate a patchwork of inconsistent regulations,” according to the ruling.  

The law is scheduled to take effect on March 13.