The Florida supreme court on Wednesday allowed new US House districts drawn by Republicans to be used in the midterm elections, marking another victory for the GOP in a nationwide redistricting effort aimed at helping the party retain its slim House majority.

Attorneys for voters who sued had argued that the new congressional districts violate a state constitutional prohibition on partisan gerrymandering, and that the court should order the state to continue using the same districts as in the previous election. The supreme court, in a 6-1 decision, denied their request for a temporary injunction without ruling on the merits of the case. The judges said they lacked jurisdiction to intervene while the lawsuit gradually plays out in the lower courts.

Republicans already hold 20 of Florida’s 28 US House seats. The new voting districts signed into law by the Republican governor, Ron DeSantis, after a swift two-day special legislative session could improve the GOP’s chances of winning four additional seats this year.

The court’s decision provides some certainty for prospective congressional candidates, who face a Friday deadline to qualify for the state’s 18 August primaries.

James Uthmeier, the Republican attorney general, who defended the new districts in court, declared “complete and total victory” in a social media post.

Opponents expressed outrage while vowing to continue the court fight, even though it may stretch into the 2028 election cycle.

“The Florida supreme court’s failure to stop this brazen partisan power grab is not only an assault on democracy, but an abdication of its duty to the people of Florida,” said Genesis Robinson, executive director of Equal Ground, a community organizing group that sued.

The new districts are “a pretty clear partisan gerrymander”, said Amy Keith, executive director of Common Cause Florida. “We’re going to do everything we can to prevent this map from impacting further, future elections.”

Voting districts typically are redrawn after a census near the beginning of each decade. Florida is one of several Republican-led states that have undertaken mid-decade redistricting as part of Donald Trump’s plan to try to hold on to a slim House majority in November by reshaping district boundaries to the GOP’s advantage.

Florida’s legislature approved the new House map on 29 April – the same day the US supreme court weakened federal Voting Rights Act protections for minorities while striking down a majority-Black congressional district in Louisiana. Since then, several southern states have taken steps to try to eliminate minority districts that have elected Democrats.

DeSantis had called lawmakers into a special session before the high court’s ruling, but he had anticipated the eventual outcome. DeSantis’s office asserted that no racial data was used for the map he presented to the legislature. The new map, among other things, redraws a south-eastern Florida district that DeSantis’s office said was created to help elect a Black representative in an attempt to comply with the federal Voting Rights Act.

In addition to barring partisan gerrymandering, a constitutional amendment approved by Florida voters in 2010 also prohibits districts from being drawn to deny or diminish the ability of racial or language minorities to elect the representatives of their choice. It further requires districts to be compact and, where feasible, use existing political and geographic boundaries.