Democratic voters in Pennsylvania filed a lawsuit against their state Thursday, challenging the existing Congressional district map on the grounds that current boundaries give Republicans an unfair advantage in elections.

The League of Women Voters of Pennsylvania and 20 other registered Democrats representing each of the state’s 18 congressional districts filed the case, arguing that Republican lawmakers deliberately altered district boundaries to their advantage, a process known as gerrymandering.

Public Interest Law Center director Mimi McKenzie issued a statement announcing the suit, saying the map “was drawn to ensure that our general elections will be decided before voters even go to the polls on Election Day,” according to the Pittsburgh Post-Gazette.

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The 61-page complaint alleges that the current district map, redrawn by GOP lawmakers after the 2010 census, “was the product of a national movement by the Republican Party to entrench its own representatives in power by utilizing the latest advantages in mapmaking technologies and big data to gerrymander districts more effectively than ever before.”

Republicans gained the Pennsylvania governorship and both chambers of the state legislature after the 2010 election, providing them a strong advantage to redraw the map in favor of GOP candidates.

While the lawsuit takes issue with Republican-drawn maps, it also acknowledges that the Democratic Party has engaged in gerrymandering of districts.

“The lawsuit is intended to protect the rights of all voters, regardless of party affiliation,” said League of Women Voters of Pennsylvania president Susan Carty in a statement reported by The Huffington Post. “The creation of ‘safe’ seats for either party undermines the ability of all voters to elect representatives of their choosing. We are suing to make sure that elections are decided by the voters, not partisan politicians.”

The petition points to the GOP’s redistricting plan as purposely confining Democrats to 5 of the 18 districts so that by much larger margins than Republicans in the remaining districts. Democrats won an average of 77.3 percent of votes in these districts as compared to the Republicans’ 59.3, and won a majority of statewide votes of 50.8 percent in the 2012 election.

District 7 near the state’s southeast border and district 12 near Pittsburgh, both redrawn in 2011, have attracted national scrutiny. Both are held by Republicans.

Overall, Republicans hold 13 districts in Pennsylvania compared to five for Democrats.

“Wealthy special interests poured piles of dark money into Pennsylvania to ensure one-party control of redistricting after the 2010 census, and the biased maps they got make incumbents virtually unbeatable at the polls,” said Ken Myers, chair of Common Cause Pennsylvania, in a statement.

A press conference on the lawsuit will be held Thursday afternoon at the state capital in Harrisburg.