The top court on Tuesday voted six to three to allow the law, Texas Senate Bill 4 (SB4), to go immediately into effect.

Legal scholars, however, have argued that the law subverts the federal government’s constitutional authority to carry out immigration enforcement.

Rights groups have also warned it threatens to increase racial profiling and imperil the rights of asylum seekers. The American Civil Liberties Union, for instance, called SB4 “one of the most extreme anti-immigrant laws ever passed by any state legislature” in the US.

Tuesday’s Supreme Court action does not weigh the merits of the law, which continues to be challenged in lower courts. It instead vacates a lower court ruling that paused the law from going into effect.

The administration of President Joe Biden has challenged SB4 on the grounds that the law is unconstitutional.

Migrant advocates, as well as civil rights groups, have also pledged to continue the legal fight to render SB4 void.

Their challenge could eventually again reach the conservative-dominated Supreme Court, which determines matters of constitutionality.

“While we are outraged over this decision, we will continue to work with our partners to have SB4 struck down,” Jennefer Canales-Pelaez, a policy lawyer and strategist at the Immigration Legal Resource Center, said in a statement.

“The horrific and clearly unconstitutional impacts of this law on communities in Texas is terrifying.”

Tami Goodlette, the director of the Beyond Borders Program at the Texas Civil Rights Project, said the Supreme Court’s decision on Tuesday “needlessly puts people’s lives at risk”.

“Everyone, no matter if you have called Texas home for decades or just got here yesterday, deserves to feel safe and have the basic right of due process,” Goodlette said in a statement.

‘Lead us to victory in court’

Texas Governor Greg Abbott and state Attorney General Ken Paxton, both Republicans, have argued the SB4 runs parallel to, but does not conflict with, federal US law.

In a post on X on Tuesday, Abbott called the Supreme Court decision “clearly a positive development”.

Paxton, whose office is defending the law in court, said it was a “huge win”.

“As always, it’s my honor to defend Texas and its sovereignty, and to lead us to victory in court,” he wrote.

The pair have become national conservative figureheads in their criticism of the Biden administration’s border policy, an issue set to dominate the 2024 presidential elections.

Texas, a southwestern state, shares a 3,145km (1,254-mile) border with Mexico. Texas leaders have said the new law is needed to control the record numbers of irregular crossings along the border in recent years.

Signed into law in December, SB4 is an extension of Abbott’s “Operation Lone Star“, a border security programme that launched in March 2021 and has since grown into a $12bn initiative.

Under the programme, the governor has planted razor wire along the border, built a floating fence in the Rio Grande, surged the number of Texas National Guard members in the area and increased the amount of funds available to local law enforcement to target migrants and asylum seekers.

‘Chaos and abuse’

It was not clear on Tuesday if local authorities would immediately begin enforcing SB4, which makes it a state crime to cross the Texas-Mexico border outside of regular ports of entry.

Those arrested face up to six months in jail for an initial offence, with repeat offenders facing up to 20 years.

Judges are permitted to drop the charges if a person agrees to be deported to Mexico, regardless of their country of origin or if they have an asylum claim in the US.

Mexico’s government had previously decried the law as “inhumane”.

Following Tuesday’s decision, White House spokesperson Karine Jean-Pierre called the law “another example of Republican officials politicising the border while blocking real solutions”.

For its part, the nonprofit Human Rights Watch on Tuesday said the law violates US asylum obligations and federal law.

“National governments are entitled to regulate their borders so long as they comply with international human rights and refugee law,” Bob Libal, a Texas consultant at Human Rights Watch, said in a statement.

“But allowing Texas to run with its draconian system of criminalisation and returns of asylum seekers is a recipe for chaos and abuse.”