(Reuters) - Pennsylvania’s top court on Monday unveiled a new map carving out the state’s U.S. congressional voting districts, imposing a plan it said was based on “traditional criteria” after rejecting a proposal drawn up by Republican lawmakers as unconstitutional.

The state Supreme Court had ruled that the Republican plan effectively marginalized likely Democratic voters. As a result, the Republicans have a more than 2-1 advantage in the state’s U.S. House of Representatives delegation, even though the number of registered Republicans and Democrats in Pennsylvania is roughly even.

The court-imposed plan could help Democrats who want to gain control of the U.S. Congress in the November midterm elections.

The new map "is composed of congressional districts which follow the traditional redistricting criteria of compactness, contiguity, equality of population, and respect for the integrity of political subdivisions," the court's order said. (bit.ly/2FeQtPJ)

State Republican leaders condemned the new map, saying the court was usurping the powers of the legislative and executive branches.

“We anticipate further action in federal court” to challenge the new boundaries, state Senate President Pro Tempore Joe Scarnati and state House Speaker Mike Turzai said in a statement.

Susan Carty, president of the League of Women Voters of Pennsylvania, which was among 19 plaintiffs in the lawsuit, said lawmakers should heed the ruling.

“To avoid future gerrymanders and court intervention, the legislature should now work toward creating an independent, impartial and accountable redistricting process,” she said in a statement.

The justices redrew the boundaries with the help of independent experts after Democratic Governor Tom Wolf last week rejected a proposal drawn by Republican legislative leaders as unfairly skewed in their party’s favor.

Legal battles are playing out in several U.S. states over gerrymandering, the process by which district lines are manipulated to favor one party. Pennsylvania has long been seen as one of the worst offenders, with one of its districts nicknamed “Goofy Kicking Donald Duck,” a reference to a cartoon image evoked by its odd shape.

Pennsylvania is a hotly contested swing state, and the redistricting is expected to boost Democrats’ chances of winning several of the U.S. House seats in the state in November.

Democrats must gain 24 seats nationwide to take control of the House from Republicans. Republicans hold 13 of Pennsylvania’s 18 congressional seats.

The new map means that Democrats could win up to 11 seats in Pennsylvania in midterm elections, said Michael Li, a lawyer with the Brennan Center for Justice at New York University’s law school, which filed an amicus brief in the case.

“This is the map that many people think is natural for Pennsylvania, which is a 50-50 state, a classic battleground, but hasn’t performed that way in terms of congressional elections for decades,” he said by telephone.

The Republican-controlled legislature created the current map in 2011, after the 2010 U.S. census. The U.S. Supreme Court has rejected Republicans’ appeal of the state court’s ruling in January striking down the boundaries.