The Supreme Court ruled against North Carolina Republicans on Tuesday, saying state legislatures do not have the sole authority to set rules for federal elections without interference from state judges.

The 6-3 decision in Moore vs. Written by Chief Justice John G. Roberts Jr., Harper rejected the GOP’s claim that state legislatures alone set the rules.

“When state legislatures prescribe the rules regarding federal elections, they remain subject to the ordinary exercise of judicial review by the state,” he wrote. “State courts retain the power to apply state constitutional limitations when legislators act under the power granted to them by the Election Clause.”

Judges Clarence Thomas, Samuel A. Alito Jr. and Neil M. Gorsuch disagreed.

The decision will make it more difficult for the dominant political party to gerrymander districts’ voting cards to get the most seats.

Democrats and many public interest advocates feared that the conservative court would strengthen GOP lawmakers and potentially allow them to defy the will of voters in the 2024 presidential race by electing a list of Republican voters, even if the Democratic candidate wins more votes in their state.

Usually, disputes over state electoral laws are resolved by state judges and the state Supreme Court. Until recently, the state’s Supreme Court was believed to have the final say on state laws.

But Republican lawmakers argued that the U.S. Constitution sets a different rule for elections of federal officials. They pointed to the clause saying that the “times, places, and manners” of electing senators and representatives “shall be prescribed in each state by the legislature thereof.”

Citing this provision, they argued that state supreme courts lacked the authority to override election rules set by state legislatures. This has been called the “independent state legislature theory”.

The Constitution has a similar provision for the election of the president. It says that “each state shall nominate” the electors who elect the president “in such manner as the legislature may direct.”

All states have passed laws that say their voters will be elected based on the outcome of the popular vote in the state.

But after President Trump lost his reelection bid to then-candidate Joe Biden in 2020, he and some of his supporters urged Republican state lawmakers to defy the law and nominate voters for Trump, not Biden. However, nobody did.

Democrats and many suffrage experts expressed alarm that if the Supreme Court upheld Republicans’ claim that state lawmakers had “independent” authority over elections, GOP lawmakers could select a list of Republican voters, even if the Democratic candidate had the upper hand in a thrilling race.

The issue came before the Supreme Court last year in a dispute over partisan gerrymandering by North Carolina Republican state legislators. They drew a ballot map that would have given the GOP a clear lead in 10 of the state’s 14 districts for electing U.S. representatives.

Common Cause sued, arguing that the map was highly partisan and did not reflect the views of the state’s voters. They won for the state Supreme Court, which then had a 4-3 majority of Democratic appointees. Those judges said the state constitution promised free and fair elections, and they ordered a new map for the 2022 midterm elections. According to that map, the state elected seven Republicans and seven Democrats to the House.

But the state’s Republican leaders appealed to the U.S. Supreme Court, arguing that state judges lacked the authority to override legislatures and impose their own card for electing members of Congress.

The Supreme Court agreed to hear their appeal and the judges sounded sharply divided when they heard their arguments in December.

But the previous month, Republicans had won two seats on the state Supreme Court, giving them a 5-2 majority. Soon after, the new majority announced it would reconsider the anti-gerrymandering ruling that had enraged GOP lawmakers.

On April 28, the state court overturned the earlier ruling, saying state lawmakers were completely free to draw electoral districts to give their party an advantage. The vote was 5-2.