(Reuters) – The Ohio Supreme Court on Friday struck down the state’s new congressional map for illegally favoring Republicans over Democrats and ordered new lines drawn, a decision that could have a significant impact on the battle for control of Congress in November’s elections.

Electoral analysts had said the Republican-backed map would ensure the party won at least 12, and perhaps 13, of the state’s 15 congressional seats, in part by splitting Cincinnati’s county into multiple districts to dilute Democratic voting power there.

In a 4-3 decision, the state’s high court found that the map violated new provisions in the Ohio constitution that were approved by voters in 2018, including language that prohibits any map that “favors or disfavors a political party or its incumbents.”

“When the dealer stacks the deck in advance, the house usually wins,” Justice Michael Donnelly wrote for the majority. “That perhaps explains how a party that generally musters no more than 55 percent of the statewide popular vote is positioned to reliably win anywhere from 75 percent to 80 percent of the seats in the Ohio congressional delegation.”

The court’s three Democrats were joined in the majority by Chief Justice Maureen O’Connor, a Republican. Three Republican justices dissented from the decision, arguing that the court was encroaching on the authority of the state legislature.

Under U.S. law, states must redraw congressional lines every 10 years to account for changes in population. In most states, legislatures oversee the process, leading to the practice of gerrymandering, in which one party engineers political maps for partisan advantage.

There are more than a dozen pending lawsuits challenging congressional maps in several states. In North Carolina, a three-judge panel earlier this week rejected Democratic claims that the state’s new congressional map illegally favored Republicans, though the plaintiffs are appealing the decision to the state Supreme Court.

Republicans need to flip only a few seats in the November 8 elections to retake control of the U.S. House of Representatives, where Democrats hold a 221-212 edge including vacancies.

Two days ago the Ohio Supreme Court also invalidated Republican-drawn maps for the state legislature’s two chambers, finding they, too, were unconstitutional gerrymanders.

The office of Governor DeWine, a Republican who approved the map, did not immediately respond to a request for comment. The state’s Republican legislative leaders could not immediately be reached for comment.

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Image: Reuters/Jonathan Drake