A panel of federal judges blocked Louisiana on Tuesday from using a newly drawn congressional map that had been designed to form a second district with a majority of Black voters, creating uncertainty just months before an election that could play a critical role in determining the balance of power in the House of Representatives.

The new districts had been outlined in January during a special session of the State Legislature. Lawmakers had been ordered to sketch out the new boundaries after a three-judge panel of the U.S. Court of Appeals for the Fifth Circuit found that the previous map had very likely violated the Voting Rights Act by diluting the voting power of Black residents.

But in a 2-to-1 decision released on Tuesday, a separate panel of federal judges sided with challengers to the new map who argued it was an “impermissible racial gerrymander” that violates the Equal Protection Clause of the 14th amendment of the U.S. Constitution.

The challenge had been brought by a group of residents scattered across the newly formed district who described themselves as “non-African American” voters. They argued that lawmakers had moved to “segregate voters based entirely on their races,” and to achieve that they stitched together “communities in far-flung regions of Louisiana.”

Critics assailed the ruling on Tuesday, saying that it threatened vital protections for voters of color. “The court’s ruling today unnecessarily puts Louisianians’ right to vote in a very precarious position,” Eric H. Holder Jr., the former U.S. attorney general and current chairman of the National Democratic Redistricting Committee, said in a statement.

The court will holding a hearing on May 6 to discuss which boundaries will be used in the coming election.

“We will of course be seeking Supreme Court review,” Louisiana’s attorney general, Liz Murrill, wrote on social media. “I’ve said all along the Supreme Court needs to clear this up.”