In a blow to Democrats' chances of maintaining a majority in the U.S. Congress, New York's highest court on Wednesday ruled the state's new congressional map was unconstitutionally designed to favor Democrats and ordered the lines redrawn.

Republicans are widely seen as favored to flip the minimum five seats they need nationwide to capture a U.S. House of Representatives majority in November's congressional elections, enabling them to block much of Democratic President Joe Biden's agenda for the remaining two years of his first term.

Democrats had hoped the aggressive New York map would offset Republican gains in states such as Texas and Florida, where Republican-controlled legislatures approved their own partisan maps as part of the once-a-decade redistricting process that follows the decennial U.S. Census.

Instead, Republicans have built a slight advantage with 46 states having completed redistricting. Only New Hampshire and Missouri have yet to approve new districts, while a state judge on Monday threw out the Republican-backed Kansas map as illegally partisan.

The New York plan, approved by Democratic super-majorities in the state's legislature, would have given the party the edge in 22 of the state's 26 seats, ousting half of the state's eight Republican members of the U.S. House.

In its decision on Wednesday, the state Court of Appeals ordered the trial judge who first ruled the map illegal last month to take over the process of drawing a new map, with assistance from a court-appointed special master.

Congressional primary elections will likely have to be moved from June to August to allow time for a new New York map, the court wrote.

In a statement, a spokesperson for the Democratic state Senate majority said Democrats disagreed with the court and would make their case to the special master.

Republican former New Jersey Governor Chris Christie, who co-chairs the National Republican Redistricting Trust, the party's main redistricting arm, told reporters that whatever map emerges will be "significantly worse" for Democrats.

New York voters in 2014 approved a new redistricting commission that was intended to insulate the process from political considerations, as well as language expressly prohibiting districts drawn to favor one party over another, a strategy known as partisan gerrymandering.

But the commission failed to produce a consensus map after its members ended in stalemate along party lines, giving Democratic lawmakers the opportunity to step in.

A four-judge majority of the seven-member Court of Appeals ruled on Wednesday that Democrats violated 2014 constitutional amendments both procedurally, by taking over when the commission stalled, and substantively, by ignoring the ban on gerrymandering.

Two judges dissented, writing that they were not convinced the map was unconstitutional. A third judge agreed that lawmakers did not have the authority to substitute their own map for the work of the commission but did not opine on whether the districts were unconstitutionally partisan.

Democratic governors appointed all seven members of the court.

The decision also invalidated the new state Senate map, which will be redrawn as well.