If Pennsylvania's Supreme Court order stands and a new map is produced, it would be used for April's primary election.
Pennsylvania's top two Republican state senators, Joe Scarnati and Jake Corman, said Monday that the state court's decision oversteps its legal authority.
A divided Supreme Court on Monday ruled that the state's Congressional maps are illegally gerrymandered and ordered the General Assembly to immediately begin redrawing them.
The court's two-page order said the legislature has until February 9 to submit a new map to Democratic Governor Tom Wolf, who would have until February 15 to sign off. If those deadlines are missed, the court said, it will draft a new map itself, with input from the parties.
The court said the boundaries "clearly, plainly and palpably" violate the state's constitution, and blocked them from remaining in effect for the 2018 elections. They succeeded, securing 13 of 18 seats in a state where registered Democratic voters outnumber Republicans 5 to 4.
"Today's ruling by the state Supreme Court is a partisan action showing a distinct lack of respect for the constitution and the legislative process", the lawmakers said in a joint statement.
"It's well established that the United States Supreme Court does not review decisions of state force that exclusively construe state law", attorney Stanton Jones said. The high court has never struck down an electoral map as a partisan gerrymander. That Republican-led court is now looking at two other cases from Maryland and Wisconsin.
"It shows there may be a second front in the war against gerrymandering that does not depend on what the U.S. Supreme Court does or does not do in the Wisconsin and Maryland cases", Li said.
The group alleged that Republicans acted in secret in 2011 to design a map that deliberately packed Democratic voters into five districts, maximizing the GOP advantage everywhere else.
Earlier this month, a federal court struck down GOP-drawn maps in North Carolina, saying Republican lawmakers violated the Constitution when they redrew numerous maps to lean so heavily in favor of Republicans. With a new Pennsylvania map, Democrats would likely have a much better opportunity to pick up several House seats.
Opponents of the map argued the state legislature violated the state's constitution by drawing House districts to expressly benefit Republicans.
They also said the state court has set up an impossible deadline of February 9 to redraw the map and that will "introduce chaos in the upcoming congressional election". The court said in its order that that race will proceed under the old congressional map.