The latest decision, from the Pennsylvania Supreme Court, struck down the state’s congressional map, saying it “clearly, plainly and palpably” violated the state’s Constitution. The court told state lawmakers to redraw the state’s 18 House districts, which currently favor Republicans, and it left open the possibility that it would impose its own map.

Under the current map, Republicans control 13 of those 18 seats. Election law experts say that a nonpartisan map could move as many as three of those seats to Democrats and increase that party’s chances of regaining control of the House in the midterm elections this fall.

The State Supreme Court’s 5-2 decision divided along partisan lines, with the Democratic justices in the majority and the Republicans in dissent. The majority has promised to issue an opinion providing its detailed reasoning but has yet to do so.

Republican lawmakers filed an emergency application last month asking the United States Supreme Court to step in, saying the case was partly governed by federal law. They pointed to Article I, Section 4 of the United States Constitution, which says that the times, places and manners of congressional elections “shall be prescribed in each state by the legislature thereof.”

The lawmakers said the State Supreme Court had thus usurped the legislature’s role in violation of federal law. They relied on a closely divided 2015 decision from the United States Supreme Court allowing an independent redistricting commission in Arizona rather than its Legislature to draw congressional districts.