What is SB4? The controversial Texas immigration law temporarily blocked by Supreme Court

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The Supreme Court has temporarily blocked a controversial Texas law that gives police the authority to arrest people they suspect of having entered the US illegally.

The new law, known as Senate Bill 4 (SB4), had been scheduled to go into effect on 9 March.

It has now been blocked until at least 13 March, giving the nation’s highest court more time to review the case.

But what does the new law involve?

SB4 is just one of Texas Governor Greg Abbott’s numerous legislative moves that seek to curb the number of undocumented immigrants coming into the US from across the state’s border with Mexico.

Under the law, migrants who enter the country illegally could be punished by up to six months in jail for a first offence. Those arrested a second time could face up to 20 years behind bars.

The legislation has been compared to Arizona’s Senate Bill 1070, the so-called “show me your papers” law that allowed police to arrest anyone they suspect of being undocumented immigrants.

The Supreme Court partially struck down SB1070 in 2012, but upheld a provision permitting police to demand anyone they believe to be undocumented to hand over their papers.

Much like with Arizona’s SB1070, opponents of SB4 say the law would likely be rooted in racial profiling.

In a statement from the American Civil Liberties Union, civil rights groups said SB4 “bypasses federal immigration authority and threatens the integrity of our nation’s constitution and laws”.

“We have long warned that this law will separate families, lead to racial profiling across the state, and harm people across the state as Governor Abbott continues his relentless campaign against people who are immigrants,” they said.

Will the law go into effect?

On Monday 4 March, the Department of Justice asked the Supreme Court to block the law, saying it would “profoundly [alter] the status quo that has existed between the United States and the States in the context of immigration for almost 150 years”.

The law stood to have “significant and immediate adverse effects” on US-Mexico relations and “create chaos” in the enforcement of federal immigration laws in Texas, the Justice Department said.

The Justice Department’s request followed a federal court ruling last week in which US District Judge David Ezra also blocked the law from being enacted.

In that 114-page ruling, Mr Ezra argued that SB4 was in conflict with federal immigration law and violated the US Constitution.

Permitting a Texas state law to supersede federal law due to an “invasion” – as Republicans have described illegal border crossings – would “amount to nullification of federal law and authority – a notion that is antithetical to the Constitution and has been unequivocally rejected by federal courts since the Civil War,” Mr Ezra wrote.

However, the law could still take effect in a matter of days as the Supreme Court’s temporary pause on the law is only in place until 13 March.