The lawsuit was expected in a fight over the map Democrats got to draw because they control the Illinois Legislature and the governor's office. Republican state lawmakers filed a federal lawsuit last week over the legislative map for new Illinois House and Senate districts because of the damage it could impose.
Democrats have defended both maps as being fair. Gov. Pat Quinn signed them into law last month.
"Ensuring that everyone's voice is heard in government is a fundamental part of our democracy. ... This open and transparent process resulted in a map that represents our diverse state and protects the voting rights of minorities," Quinn spokeswoman Annie Thompson said in a statement.
The latest lawsuit was filed by the Committee for a Fair and Balanced Map, a group that includes such prominent Republicans as former U.S. House Speaker Dennis Hastert, and 10 of the 11 Republicans in Illinois' congressional delegation. They claim the new map "blatantly discriminates against Latino and Republican voters."
Only GOP Republican U.S. Rep. Tim Johnson from central Illinois didn't join the lawsuit, which also names a handful of Republican and Latino voters as plaintiffs.
Johnson spokesman Phil Bloomer said while the congressman believes the redistricting was unfair and hopes a court might undo it, he's focused on other things. "These challenges have never succeeded in the past so he's decided to devote his energy and his resources to re-election," Bloomer said.
The new map could be devastating for Republicans as Democrats nationally try to retake control of the U.S. House after losing it in 2010.
The Illinois map dismantles traditional GOP areas and gives Democrats a chance to win them in the 2012 election by packing incumbent Republicans together in districts or squeezing them into Democrat-friendly districts with Democratic incumbents, according to the complaint. Illinois sent five GOP freshmen to Washington in the 2010 election, including Rep. Bob Dold, who won Republican U.S. Sen. Mark Kirk's old seat.
"The proposed congressional plan ... effectively reverses the results of the 2010 congressional elections by redrawing districts so that the citizens of Illinois that gave Republicans an 11 to 8 advantage in Illinois's congressional delegation only nine months ago would see the state's congressional delegation transformed to one with 12 Democrats and only 6 Republican," according to the complaint.
Illinois' new map has 18 instead of 19 congressional districts because of the state's slowing population growth.
Republicans also contend the map hurts Latino voters. By packing "excessive numbers" of Latinos into a new 4th Congressional District, now represented by U.S. Rep Luis Gutierrez, the map dilutes Latino voters in other districts. They accuse Democrats of a "racial gerrymander."
Republicans also contend the map was drawn to protect the white majority in some districts to save Democratic incumbents.
The Mexican American Legal Defense and Educational Fund, or MALDEF, didn't comment on the congressional map lawsuit challenge. Last week, MALDEF said it was still studying the state redistricting map after state lawmakers filed their lawsuit.
Other Latino leaders have urged support for both the state's new legislative and congressional maps, suggesting that Latino groups shouldn't join Republicans in their efforts to defeat the maps.