The Supreme Court appeared ready Tuesday to uphold voting restrictions in Arizona in a key case that could make it harder to challenge a raft of other voting measures Republicans have proposed following last year’s elections.

All six conservative justices, appointed by Republican presidents, suggested they would throw out an appellate ruling that struck down the restrictions as racially discriminatory under the landmark Voting Rights Act. The three liberal members of the courts, appointed by Democrats, were more sympathetic to the challengers.

Less clear is what standard the court might set for how to prove discrimination under the law, first enacted in 1965.  The outcome could make it harder, if not impossible, to use the Voting Rights Act to sue over measures making their way through dozens of Republican-controlled state legislatures that would make it more difficult to vote.

Civil rights group and Democrats, argue that the proposed restrictions would disproportionately affect minority voters, important Democratic constituencies.

Democrats in Congress, meanwhile, have proposed national legislation that would remove obstacles to voting erected in the name of election security.