Voting rights groups that support the Democratic Party are preparing for what they call a possible crisis if the U.S. Supreme Court weakens a key part of the Voting Rights Act, one of the most important pieces of civil rights legislation in the country.

The case that is causing the worry is Louisiana v. Callais, where the result will decide the future of Section 2 of the Voting Rights Act, which says that redistricting plans can’t make it harder for racial minorities to vote.

Politico reported that two well-known voting rights groups warned that eliminating or limiting Section 2 would allow Republican-controlled legislatures to redraw up to 19 congressional districts in their favor.

Fair Fight Action and the Black Voters Matter Fund put together a new analysis that was only shared with POLITICO. It says that if Section 2 of the Voting Rights Act is struck down, it could almost guarantee that Republicans will keep control of the House of Representatives.

The groups that wrote the paper say that it is still feasible to have a verdict before the midterm elections next year, even if it is not likely. The groups found 27 congressional seats across the country that may be redrawn to help Republicans if the current legal and political situation stays the same. Nineteen of these changes are directly related to the possible loss of Section 2 protections.

LaTosha Brown, co-founder of the Black Voters Matter Fund, said that doing so would “clear the way for a one-party system where power serves the powerful and silences the people.” She did not address the constitutional issue of drawing congressional districts based only on race, which is what the high court is looking into.

For years, Republicans have tried to reduce or do rid of Section 2 of the Voting Rights Act, which says that voting laws and redistricting can’t be based on race. They say that the rule unjustly helps Democrats by making districts with a lot of Democrats and a lot of Republicans.

The Supreme Court has turned down those arguments before, but voting rights supporters are worried that the next Louisiana v. Callais case could be a turning point.

On the other hand, Democrats might potentially try to take advantage of any changes to the statute by redrawing district borders in states that are very Democratic and yet have VRA safeguards. Politico stated that analysts think these kinds of chances would be few and far between compared to the larger redistricting benefits that Republican-controlled legislatures could get.

The Voting Rights Act is utilized in redistricting to stop racial gerrymandering that makes it harder for minority voters to have their voices heard. States usually follow the rules by designing districts that provide racial and ethnic minority groups a fair chance to vote for the candidates they want.

Politico said that many experts on election law think that the Supreme Court could limit the VRA’s reach in its next decision. This could lead to big changes in how Congress is represented in the South.

The article says that this kind of decision might lead to Democrats being kicked out of states like Alabama, South Carolina, Tennessee, and Mississippi. A lot of other states, like Louisiana, Georgia, North Carolina, Texas, and Florida, would probably still have at least one Democratic member of Congress, but the number of Democrats in Congress would go down a lot.

The research is coming out at the same time as Republicans are pushing for redistricting across the country before the November elections. The White House strongly supports this plan, which might help the GOP keep its tiny majority in the House. Redrawing the lines in the middle of the cycle is rare, although it has happened before and has already made six more Republican-leaning districts in two states.

Several other states run by Republicans are likely to do the same, and that number might climb a lot if important protections in the Voting Rights Act are taken away.

In response, Fair Fight Action and the Black Voters Matter Fund are telling Democrats to come up with a “aggressive and immediate” plan to fight Republican redistricting moves that are already happening.