Pennsylvania's top Republican lawmakers asked the U.S. Supreme Court on Thursday to stop an order by the state's highest court in a gerrymandering case brought by Democrats that threw out the boundaries of its 18 congressional districts and ordered them redrawn within three weeks.

Republicans who control Pennsylvania's Legislature wrote that state Supreme Court justices unconstitutionally usurped the authority of lawmakers to create congressional districts and they asked the nation's high court to put the decision on hold while it considers their claims.

The 22-page argument acknowledged that "judicial activism" by a state supreme court is ordinarily beyond the U.S. Supreme Court's purview. But, it said, "the question of what does and does not constitute a 'legislative function' under the Elections Clause is a question of federal, not state, law, and this Court is the arbiter of that distinction."

Justice Samuel Alito, who handles emergency appeals from Pennsylvania, could ask the registered Democratic voters on the other side of the case to respond. Alito could act on his own, though the full court generally gets involved in cases involving elections. An order could come in a matter of days, although there is no deadline for the justices to act.

Pennsylvania's congressional districts are criticized as among the nation's most gerrymandered. Its case is happening amid a national tide of gerrymandering cases from various states, including some already under consideration by the U.S. Supreme Court.

Election law scholars call the Republicans' request for the U.S. Supreme Court's intervention a long shot.

They say they know of no other state court decision throwing out a congressional map because of partisan gerrymandering, and the nation's high court has never struck down an electoral map as a partisan gerrymander.