By Jon Herskovitz and Jim Forsyth

SAN ANTONIO (Reuters) – A small border town and some of the largest cities in Texas will ask a federal judge on Monday to block a new state law to punish “sanctuary cities,” arguing it promotes racial profiling, diverts resources from police and is unconstitutional.

The Republican-backed law in Texas, the U.S. state with the longest border with Mexico, takes effect on Sept. 1. It is the first of its kind since Republican Donald Trump became president in January, promising to crack down on illegal immigration.

Luis Vera, an attorney for the League Of United Latin American Citizens, one of the numerous plaintiffs in the suit, said the bill was signed despite opposition from several police chiefs across Texas and the state’s large Latino population.

“No one in the history of the United States has ever attempted this in any state. That’s why the whole world is watching us right now,” Vera said in an interview.

The law known as Senate Bill 4 calls for jail time for police chiefs and sheriffs who fail to cooperate in U.S. immigration enforcement. The measure also allows police to ask about immigration status during a lawful detention.

Supporters have said immigrants who do not break the law have nothing to fear. Critics contend it allows police to detain people for up to 48 hours for immigration checks, even for minor infractions such as jaywalking.

“It is absurd, it is offensive, when people say sanctuary cities make us safe. They allow hardened criminals to hide in plain sight,” Republican Lieutenant Governor Dan Patrick told reporters last week.

The hearing in the U.S. District Court for the Western District of Texas in San Antonio will be before Judge Orlando Garcia.

In a separate case this month, Garcia cast doubt on the legality of some Immigration and Customs Enforcement (ICE) detainer requests at the heart of the law, saying there are times when they can violate the U.S. Constitution.

A detainer is a request by immigration officials for a jurisdiction to continue to hold a person in custody, usually for no more than 48 hours, to check if they can be handed over to ICE for potential deportation.On Friday, The Trump administration filed court papers to support the Texas state law and is seeking to argue in court hearings in favor of the legislation it says will help keep America safe.

(Reporting by Jon Herskovitz and Jim Forsyth; Editing by Phil Berlowitz)