A liberal-leaning government watchdog group on Friday filed suit over North Carolina congressional districts they say give Republicans an unfair advantage, launching a new round of litigation that could have far-reaching effects for years to come.

The lawsuit, filed by Common Cause in U.S. District Court, alleges Republicans in the North Carolina state legislature improperly considered the partisan makeup of each district when they redrew district lines earlier this year. Under those lines, Republicans are likely to win ten of the state’s 13 House seats in November.

“Perhaps for the first time ever in North Carolina, state legislators have freely and publicly admitted that they gerrymandered for rank partisan advantage,” Common Cause NC executive director Bob Phillips said in a statement announcing the lawsuit.

If the court sides against North Carolina Republicans, it could open the floodgates to legal challenges in other states where Democrats and Republicans have drawn lines with clear partisan intent.

North Carolina Republicans drew the current boundaries after a federal court ruled their earlier lines, drawn after the 2010 Census, improperly diminished the political power of African-American voters. Rather than allow a federal court to rearrange district lines, state legislators in February offered a quick fix that satisfied federal courts while maintaining the ten Republican, three Democrat mix of the state’s congressional delegation.

During that February process, state Sen. Bob Rucho (R) and state Rep. David Lewis (R), co-chairs of a joint redistricting committee, acknowledged those who drew the new maps were using political data, such as past election results and voter registration statistics. Earlier criteria adopted by the legislature instructed mapmakers to make a “reasonable effort” to maintain the ten Republican, three Democrat split.

Common Cause says those instructions violate several sections of the Constitution, including the First and Fourteenth Amendments and parts of Article One.

A spokesman for state legislative Republicans did not immediately respond to a request for comment on Saturday.

Common Cause submitted past election results to show that the lines as previously drawn overwhelmingly favored Republicans. In 2014, North Carolina Republicans won 55 percent of the votes for U.S. House seats, but they held 77 percent of the districts. In 2012, Democrats won 51 percent of all votes for House seats in the state, though they won only four of thirteen districts.

The suit isn’t the first time Common Cause has sued over partisan gerrymandering. The group challenged Maryland congressional districts after the Democratic-led legislature drew a map that gave their party an extra seat. That case, Shapiro v. McManus, is awaiting arguments before a three-judge panel in the 4th Circuit Court of Appeals.