Testing the limits of how far Texas can go to keep migrants out of the US, Republican Governor Greg Abbott on Monday signed into law sweeping new powers that allow police to arrest migrants who cross the border illegally and give local judges authority to order them to leave the country.

Opponents have called the measure the most dramatic attempt by a state to police immigration since a 2010 Arizona law — denounced by critics as the “Show Me Your Papers” bill — that was largely struck down by the US Supreme Court. Texas’ law is also likely to face swift legal challenges.

Immigration enforcement is a federal responsibility. But Texas Republicans have increasingly blurred those boundaries under President Joe Biden, saying his administration isn’t doing enough to stop people from entering the country illegally. Texas has bused more than 65,000 migrants to cities across America and installed razor wire along the banks of the Rio Grande, which has snagged and injured some asylum-seekers.

Separately Monday, US Customs and Border Protection temporarily shut down two railroad border crossings in Texas to shift officers to helping process migrants. Rail operators said the closures at Eagle Pass and El Paso would hamper trade ahead of Christmas.

The new law signed by Abbott allows any Texas law enforcement officer to arrest people who are suspected of entering the country illegally. Once in custody, they could either then agree to a Texas judge’s order to leave the US or be prosecuted on misdemeanor charges of illegal entry. Migrants who don’t comply could face arrest again under more serious felony charges.

Legal experts have called the measure a violation of the US government’s purview over immigration enforcement. Mexico’s government also rebuked the measure. In the US, some immigrant rights groups have lashed out at Biden for not stopping Texas’ aggressive border measures sooner.

Thirty former US immigration judges, who served under both Republican and Democratic administrations, signed a letter this month condemning the measure as unconstitutional.

“This is sanctioned racial profiling and all Texans must stand up and demand this measure, that will no doubt cause massive family separations, be struck down,” said Priscilla Olivarez, an attorney and strategist for the San Antonio-based Immigrant Legal Resource Center

During debate in the Texas House, GOP state Rep. David Spiller pushed back against concerns that the law would be used as a dragnet to arrest immigrants statewide. He said enforcement would mostly take place in border counties and rebuffed efforts by Democrats to narrow the law, including a proposed carve-out for police on college campuses.

“This is not, ‘Round up everyone who is here illegally and ship them back to Mexico,'” he said.

Under bilateral and international agreements, Mexico is required to accept deportations of its own citizens, but not those of other countries. Under the Texas law, migrants ordered to leave would be sent to ports of entry along the border with Mexico, even if they are not Mexican citizens.

“The Mexican government categorically rejects any measure that would allow local or state authorities to detain or deport Mexicans or other nationalities to Mexican soil,” Mexico’s foreign relations department wrote in a statement.

Opponents have accused Texas Republicans of using the law as a vehicle to force the Supreme Court’s new conservative majority to revisit the landmark Arizona decision in 2012. At the time, Justice Anthony Kennedy said Arizona may have “understandable frustrations” with immigrants who are in the country illegally but can’t pursue policies that “undermine federal law.”

Earlier this month, Abbott endorsed former President Donald Trump, the Republican presidential front-runner in 2024. Over the weekend, Trump delivered alarming anti-immigrant remarks about “blood” purity, echoing Nazi slogans of World War II.