COLUMBIA -- Six black voters on Friday filed a lawsuit challenging new U.S. House district lines and called the work of the GOP-dominated Legislature "voting apartheid."

The voters living in Florence, Sumter, Georgetown, Berkeley, Darlington and Charleston counties are suing Gov. Nikki Haley, the Legislature and other state officials and claim a race-based plan for the state's seven districts "creates a system of voting apartheid in South Carolina that segregates white and black voters into election districts" and packs black voters into one congressional district.

"This racial quota system has resulted in elections that are always or almost always decided by the district's majority race," the lawsuit says.

The suit filed in U.S. District Court asks for a three-judge panel to throw out the plan, make lawmakers draw a new one and bar any elections based on them.

The U.S. Justice Department last week told legislators it would not challenge the district layout. But that doesn't mean other groups can't take the plans to court.

Redistricting is a once-a-decade process to make sure political district lines reflect population changes revealed by the U.S. Census. South Carolina is picking up a seventh U.S. House seat — something the Palmetto State had years ago, before population fell in 1930. That new district was added to the state's northeastern corner on the coast and the state line with North Carolina.

The proposed maps for South Carolina and other Southern states require federal approval under the Voting Rights Act because of a history of inequitable treatment of black voters.

When the Justice Department said last week that it wouldn't challenge South Carolina's U.S. House plan, state Democratic Party Chairman Dick Harpootlian said the redistricting plan would wind up in court. He's also preparing challenges for districts drawn for state House and Senate seats.

Harpootlian, a top Democratic lawyer who has handled similar cases in the past, is representing the plaintiffs. But he said the lawsuit is not being undertaken by his party. The Legislature, he said, added black voters to U.S. Rep. Jim Clyburn's majority black district and expanded its geographic boundaries.

"The congressional reapportionment plan passed by this Legislature and signed by this governor is racial apartheid in that it segregates our state by congressional districts," Harpootlian said.

During the state Senate debate, Democratic legislators questioned whether Republicans were packing black voters into Clyburn's district. Senate Democratic Caucus spokesman Phil Bailey said the caucus hasn't decided whether it will join the litigation.

State GOP Chairman Chad Connelly questioned the motives. "South Carolina's new congressional districts were crafted with the utmost care. Today's lawsuit is misguided and purely politically motivated," Connelly said.

Clyburn, the senior member of the state's delegation to Washington and the U.S. House's third-highest ranking member, now has a district that spans much of the state and has 55 percent black population. The district stretches from Williamsburg County near the coast to Allendale County on the state's western border on the Savannah River with Georgia. He'll represent Calhoun, Clarendon, Hampton and Jasper and parts of Beaufort, Berkeley, Charleston, Colleton, Dorchester, Florence, Orangeburg, Richland and Sumter counties.

The lawsuit notes that four of the five remaining congressional districts are left with fewer black voters.

Harpootlian said Clyburn's district lines zig and zag with no explanation other than race for why people who otherwise share little in common are included.

In the other districts, he said, large groups of voters were kept together based on geography, including county or city lines.

Harpootlian has said the Justice Department is using an antiquated standard as states draw district lines to maintain black-majority districts. He said time and again voters in the South are giving more support to candidates without regard to their race. He notes as an example that U.S. Rep. Tim Scott, a black Republican, won the state's 1st District last year.