A Maryland judge ruled on Wednesday that state Democrats used a flawed process in crafting an amendment that would change the rules for redrawing congressional maps. The decision, if it stands, would imperil any attempt at redistricting before the 2028 election.

The judge, Robert J. Thompson of Anne Arundel County Circuit Court, ruled that the measure should no longer be put to voters in a November referendum. But he stayed the ruling, acknowledging that it would be appealed to the Maryland Supreme Court. The court may act quickly, given that the Maryland Board of Elections has said that ballots are slated to begin printing on Sept. 3.

“Today’s ruling is an important victory for the rule of law and for every Maryland voter who expects government to follow the Constitution and the election laws it enacts,” said Steve Hershey, the minority leader in the State Senate and a Republican.

Democratic state leaders quickly appealed, as the judge had anticipated. “We believe Maryland voters deserve the opportunity to make their voices heard, and we will continue fighting to ensure they can,” said Ammar Moussa, a spokesman for Gov. Wes Moore.

The ruling marks the third time this year that state judges have blocked Democratic attempts at gerrymandering. In May, judges in Virginia struck down a new congressional map days after the state’s voters had approved it in a referendum. Judges in Colorado blocked Democratic redistricting measures in June, ruling that the proposals, as worded, had violated the State Constitution.

In all of these cases, Democratic state leaders were pushing to redraw congressional maps as part of a nationwide battle of redistricting initially set off by President Trump.

Early last summer, Mr. Trump pushed Texas lawmakers to redraw state maps to give Republicans an advantage ahead of the 2026 midterms. Several states followed suit, including North Carolina, Missouri and Florida, all of which have Republican-controlled legislatures. But in some Democratic-led states, like California and Virginia, the effort came with an added obstacle: amendments in the State Constitution intended to curb gerrymandering.

While California was successful in revising its Constitution and adopting a new map, the Virginia Supreme Court ruled in May that state lawmakers had not followed the right procedures in getting the amendment on the ballot.

The possibility of judicial roadblocks is precisely what slowed the process down in Maryland. Democrats hold seven of the state’s eight congressional seats, but Democratic leaders, including Mr. Moore and U.S. Representative Hakeem Jeffries, the party’s leader in the House, pushed state lawmakers to draw a new map that would make that last seat easier to pick up.

Bill Ferguson, the president of the State Senate, who is also a Democrat, resisted the push for months. He warned that any attempt at a new map is likely to be blocked by a judge — as had happened in 2022. But after the U.S. Supreme Court gutted the Voting Rights Act in April, Mr. Ferguson said he was open to redistricting.

The first step was the passage of a constitutional amendment that would remove federal redistricting from the oversight of state judges. The legislature passed such a measure earlier this month, aiming to put it before voters in November. If approved, the legislature would be able to redraw the state’s congressional map before the 2028 elections.

But Republicans quickly challenged the amendment in court, arguing among other things that the state legislature had passed a law this year requiring petitioned ballot questions to be certified by the secretary of state by July 1. In court, lawyers for the Moore administration argued that this rule did not apply when the ballot question was formulated directly by the state legislature.

Judge Thompson, who was appointed by a Republican governor, disagreed. He ruled that the process was deficient “because the legislature did not follow the very laws it enacted.” The judge also took issue with the wording of the amendment itself, finding it “intentionally misleading.”

Mr. Ferguson said in a statement that he was confident that the state Supreme Court would issue “a clear ruling that affirms the General Assembly’s constitutional authority.”