All three districts are so politically lopsided that the three Democratic incumbents overwhelmingly won re-election in 2012.

Rep. Mel Watt got 80 percent of the vote in District 12; Rep. G.K Butterfield got 75 percent in District 1, and Rep. David Price got 74 percent in District 4.

Both the 1st district and 12th district have black majorities. The share of black voters increased in both districts after redistricting, according to the Census Bureau.

Two lawsuits were filed in late 2011 to challenge the districts. The lawsuits allege the boundaries are unconstitutional racial gerrymanders that cluster black voters in the districts so that seats around them are more likely to elect Republicans.

"I think Republicans got very greedy," said Scott Falmlen, a former executive director of the North Carolina Democratic Party. "They just went to the extreme to maximize their power."

Republicans say the districts are lawful and were designed to protect the state from legal claims under the Voting Rights Act, which generally prohibits states from diluting the voting power of racial and ethnic minorities. Republicans note that the Justice Department signed off on the maps and decided not to challenge them.