A coalition of left-leaning organizations urged Gov. Nathan Deal and lawmakers to scuttle a House Republican plan to redraw the district boundaries of eight Republicans and one Democrat, warning it could be ruled unconstitutional because it shifts thousands of minority voters out of the areas.

In a letter sent Tuesday to state leaders, the groups said the redistricting plan outlined in House Bill 515 is "likely illegal" and urged legislators to wait until after the 2020 U.S. Census to make major revisions to the maps. (You can read the letter here.)

"If HB 515 is signed into law, Georgia will likely be in violation of the Voting Rights Act and subject to litigation that has cost states like Virginia and Texas millions of dollars," the groups wrote. "This would cast a dark shadow over our state."

The measure was approved this month by the House, largely along party lines, and is now pending in the Senate, which is expected to add its own district changes. The changes help a pair of Republicans whose districts have steadily become more competitive: state Reps. Rich Golick and Brian Strickland.

The liberal advocacy group ProGeorgia conducted an analysis on Golick's district and Strickland's district that found thousands of minority voters were being drawn out of the district and thousands of white voters were added.

It has also drawn criticism from former U.S. Attorney General Eric Holder, who now chairs the National Democratic Redistricting Committee and accused Republicans of shifting black voters out of swing districts to protect the two incumbents.

“The Georgia House’s last-minute power grab is political map-rigging at its worst," Holder said.

Republican supporters said the redistricting was aimed at bundling communities and neighborhoods of interest together. The legislation's sponsor, state Rep. Johnnie Caldwell, said there was nothing "sinister" about the proposal.

Asked about the measure before the vote, House Speaker David Ralston invoked a Democratic plan to redraw legislative districts in the early 2000s that was tossed by a federal judge.

“I look for something a little more persuasive than what I’ve been hearings so far today,” he said of Democratic criticism. “The proposals – I’ve looked at them – and they hurt no member of the House of Representatives at all. Period.”