The US Supreme Court delivered a major victory for voting rights advocates on Thursday, ruling that Alabama’s congressional map violated the Voting Rights Act of 1965 by discriminating against Black voters.

In a 5-4 decision, the court upheld a lower court’s finding that the state’s Republican-controlled legislature had drawn the map in a way that reduced the influence of Black voters, who make up about a quarter of the state’s population.

The court rejected Alabama’s argument that it had to comply with a different provision of the Voting Rights Act that required it to maintain the existing number of majority-Black districts.

The court said that this argument ignored the “totality of circumstances” that showed that the map diluted the voting power of Black voters and prevented them from electing their candidates of choice.

The court also refused to adopt a new standard for evaluating claims of vote dilution under Section 2 of the Voting Rights Act, which prohibits voting practices that result in racial discrimination. The court said that Alabama’s proposed standard was “neither compelling in theory nor in practice” and would undermine the purpose of the law.

The decision was written by Chief Justice John Roberts, who was joined by Justice Brett Kavanaugh and the three liberal justices. Roberts, who has been a critic of the Voting Rights Act in the past, wrote that the court was not changing its longstanding interpretation of Section 2, but rather applying it to the facts of the case.

The decision means that Alabama will have to redraw its congressional map to create a second district where Black voters have a realistic chance of electing their preferred candidates.

The ruling also has implications for other states, such as Louisiana, Texas and Georgia, where similar lawsuits are challenging congressional maps for diluting the voting power of minority voters.