Alito, who was nominated by Republican President George W. Bush in 2005, rejected a stay request from state GOP legislators and Republican voters to block the Pennsylvania Supreme Court's ruling last month that the congressional map unfairly favored Republicans. On Jan. 22, the Democratic-dominant state justices, in a 4-3 ruling, ordered the legislature to redraw the borders and submit a plan to the governor, Gov. Tom Wolf, a Democrat, by Feb. 9 and the court by Feb. 15. If the deadlines aren't met, the court will draw its own map "based on the evidentiary record developed."
The midterm primaries are May 18. Republicans have won 13 of the state's 18 congressional seats since 2012 even though Democrats have won statewide races, including in the U.S. Senate. President Donald Trump narrowly won the state in 2016.
The Republicans, according to court procedure, could still seek a reconsideration of Alito's ruling by another justice but second attempts usually are referred to the full court.
The state high court based its opinion on its Constitution, which the nation's highest court doesn't have authority on its meaning.
But the Republicans said the ruling violated the U.S. Constitution because it denies the legislature of its power to draw voting maps.
"'Redistricting involves lawmaking in its essential features and most important aspect,'" the lawmakers wrote, quoting Supreme Court precedent. "But for the first time in United States history, a state court, in attempting to play the role of 'lawmaker,' has invalidated a congressional districting plan without identifying a violation of the U.S. Constitution or a state constitutional or statutory provision providing specific redistricting criteria."
U.S. Supreme Court justices have rejected similar orders in cases involving other states.
But last month, the U.S. high court halted a lower federal court ruling based on federal law that ordered the North Carolina legislature to redraw its congressional map. The North Carolina decision, as well as cases in Wisconsin and Maryland, directly raised issues that are before the high court.