HOUSTON, Feb. 29 -- A federal judge on Thursday blocked a new Texas state law allowing Texas police to arrest migrants crossing the U.S.-Mexico border illegally.

The Texas law, known as SB4, set to take effect on Tuesday next week, is "patently unconstitutional" and "conflicts with key provisions of federal immigration law, to the detriment of the United States' foreign relations and treaty obligations," U.S. Judge David Ezra based in Austin wrote.

Immigration enforcement is solely within the jurisdiction of the federal government, the judge noted in a preliminary injunction that will keep it from being enforced until the court battle concludes.

"SB4 threatens the fundamental notion that the United States must regulate immigration with one voice," the judge wrote.

The federal government "will suffer grave irreparable harm" if the Texas law takes effect since it could inspire other states to follow suit, creating inconsistent patchwork of rules about immigration, Ezra warned.

If Texas arrested and deported migrants who may be eligible for political asylum, the state would violate the Constitution and also be "in violation of U.S. treaty obligations," the judge added.

In response, Texas appealed the ruling to the conservative 5th U.S. Circuit Court of Appeals, local media reported.

Immigrant rights groups filed a lawsuit against the Texas law one day after the state's Governor Greg Abbott signed the bill in December.

According to the plaintiffs, the bill violates the federal constitution since Congress has given the federal government sole authority over immigration enforcement. It will also prevent immigrants from requesting asylum in the country, a civil right they have regardless of how they enter the United States.

The American Civil Liberties Union (ACLU) and the Texas Civil Rights Project filed the lawsuit in an Austin federal court on behalf of El Paso County, the largest border county in Texas, as well as two other immigrant rights organizations -- El Paso-based Las Americas Immigrant Advocacy Center and Austin-based American Gateways.

Under the law, state law enforcement officers will be authorized to arrest migrants who cross the border illegally.

Afterward, the detained migrants could either agree to a Texas judge's order to leave the country or be prosecuted on misdemeanor charges carrying a punishment of up to six months in prison. Repeat offenders could face more serious felony charges with a punishment of two to 20 years in jail.

Up to 30 former U.S. immigration judges, who served under both Republican and Democratic administrations, signed a letter earlier this month condemning the measure as unconstitutional.

The law also seeks to require state judges to order migrants returned to Mexico if they are convicted; local law enforcement would be responsible for transporting migrants to the border. A judge could drop the charges if a migrant agrees to return to Mexico voluntarily.

The lawyer representing Texas, Ryan Walters, argued that the high number of migrants arriving at the border -- some of them smuggled by drug cartels -- constitutes an invasion and Texas has a right to defend itself under Article I, Section 10 of the U.S. Constitution, which prohibits states from engaging in war on their own "unless actually invaded."

  - Xinhua