The US supreme court has ruled that Louisiana will have to redraw its congressional map, in a landmark decision that effectively guts a major section of the Voting Rights Act.

In a 6-3 decision along partisan lines, the court rendered ineffective section 2 of the Voting Rights Act, the last remaining powerful provision of the 1965 civil rights law that prevents racial discrimination in voting. Section 2 has long been used to ensure minority voters are treated fairly in redistricting.

“Allowing race to play any part in government decision-making represents a departure from the constitutional rule that applies in almost every other context,” justice Samuel Alito, a conservative, wrote for the majority opinion.

“Compliance with section 2 thus could not justify the state’s use of race-based redistricting here. The state’s attempt to satisfy the middle district’s ruling, although understandable, was an unconstitutional racial gerrymander.”

The court’s decision is a major upheaval in US civil rights law and gives politicians permission to draw districting plans that weaken the influence of Black and other minority voters. Some states may even rush ahead to try to redraw districts in advance of this year’s midterm elections.

Asked by reporters on Wednesday whether states should redraw their congressional maps in response to the ruling, US president Donald Trump said: “I would.”

In a dissenting opinion, justice Elena Kagan wrote the court had now accomplished a “demolition of the Voting Rights Act”.

The court’s decision on Wednesday is the latest in a series that dismantled the law, she wrote, including a major decision in 2013 case, Shelby County v Holder, that nullified another major provision in the law that required places with a history of discrimination to get changes preapproved by the federal government before they went into effect.

“Under the court’s new view of section 2, a state can, without legal consequence, systematically dilute minority citizens’ voting power,” Kagan wrote in a dissent that was joined by justices Sonia Sotomayor and Ketanji Brown Jackson.

“The majority claims only to be ‘updat[ing]’ our section 2 law, as though through a few technical tweaks. In fact, those ‘updates’ eviscerate the law.

“Today’s decision renders section 2 all but a dead letter,” she continued. “The decision here is about Louisiana’s district 6. But so too it is about Louisiana’s district 2. And so too it is about the many other districts, particularly in the south, that in the last half-century have given minority citizens, and particularly African Americans, a meaningful political voice. After today, those districts exist only on sufferance, and probably not for long.”

At the heart of the case, Louisiana v Callais, was a question of how much lawmakers are allowed to consider race when they redraw districts to ensure that Black voters are adequately represented.

The supreme court initially heard oral arguments in the case last March, but took the unusual step of asking lawyers to reargue the case last fall. In setting the case for a re-argument, the justices raised the stakes of the case, asking lawyers to focus on whether section 2 of the Voting Rights Act was constitutional.

In its decision on Wednesday, the court’s majority stopped short of saying outright that section 2 was unconstitutional.

Instead, the majority significantly reworked a three-part test that plaintiffs need to pass in order to win a section 2 redistricting test. The new test is significantly harder to pass and designed to require plaintiffs to prove intentional racial discrimination – an extremely difficult burden.

“In short, section 2 imposes liability only when the evidence supports a strong inference that the state intentionally drew its districts to afford minority voters less opportunity because of their race,” Alito wrote.

Such a declaration “is not only out of line with text, it is also out of line with the history of section 2”, Richard Hasen, an election law scholar at the University of California, Los Angeles wrote in a blog post. In 1982, Congress amended the Voting Rights Act to clarify that proving intentional discrimination was not necessary to win a case under section 2.

For decades, the first part of the three-part test in a section 2 lawsuit has required plaintiffs to show the minority group alleging discrimination is large and compact enough to constitute a majority in a single-member district.

Alito’s decision adds two new requirements to this – plaintiffs may not consider race in drawing a hypothetical alternative map and must also ensure that it achieves the state’s traditional districting criteria and partisan goals.

That change alone is a major blow to the Voting Rights Act. In the US south, voting is highly racially polarised, so drawing a district that prevents racial discrimination is likely to also affect the partisan make-up of a map. It may be impossible for a state to achieve its partisan goals without discriminating against minority voters.

It also gives lawmakers virtually unlimited leeway to justify drawing districts that discriminate based on race, Kagan wrote. – The Guardian