RALEIGH — The redistricting practices of North Carolina Republicans are getting scrutinized yet again in court, this time in a trial in which federal judges must decide whether mapmakers can go too far drawing boundaries that favor their party.

A three-judge panel begins hearing evidence Monday in litigation filed by election advocacy groups, the state Democratic Party and voters who allege unlawful partisan gerrymandering in the state’s current congressional map, which favors the GOP. Those who sued want the map redone.

Several lawsuits this decade challenging districts drawn by the GOP-dominated General Assembly focused on alleged racial gerrymandering, which federal courts agreed existed. Legislative districts had to be redrawn in August, and another federal panel is deciding now whether those problems were fixed.

The plaintiffs in the congressional case, however, argue the U.S. House boundaries redrawn by the GOP in 2016 are so politically uncompetitive that they violate the free speech and equal-protection constitutional rights of voters whose partisan viewpoints are in the minority, while perhaps not so statewide.

While redrawing the congressional maps last year, a legislative committee directed that the new lines help maintain the Republicans’ 10-3 seat advantage in the state.

Plaintiffs “are represented by a congressional delegation that unfairly silences their viewpoint, and their efforts to engage their fellow citizens and elected representatives are thwarted by the plan’s extreme bias,” lawyers representing the League of Women Voters of North Carolina and some individuals wrote in their opening statement for the trial, filed Friday with the court.

In a comment which the plaintiffs cite often to bolster their case, Rep. David Lewis, one of the defendants, said last year that the map would give a 10-3 partisan advantage only “because I do not believe it’s possible to draw a map with 11 Republicans and two Democrats.”

In their opening statement, the GOP legislative leaders contend the plaintiffs don’t offer a manageable standard for courts to decide what makes for “balanced” districts and should leave resolutions over redistricting to voters, who elect legislators that approve maps.

“The remedy for concerns over political map-drawing rests with the people, not with the courts,” lawyers for the Republicans wrote. “This court should avoid entangling itself in the highly partisan, hotly disputed and inherently political process of redistricting.”

The Greensboro trial, expected to last four or five days, begins two weeks after the U.S. Supreme Court heard oral arguments in a Wisconsin case in which a lower court ruled that Republicans packed Democrats into some districts and spread them across others to entrench GOP control in the Legislature. The justices haven’t yet ruled that illegal partisan gerrymandering exists in a specific case. The phrase hasn’t been well defined.

But the plaintiffs argue that’s changed with statistical tools and a three-pronged test described in the Wisconsin arguments. Among the metrics is an “efficiency gap” that attempts to compare the statewide average share of the vote a party receives in each district with the statewide percentage of seats it wins.

North Carolina’s gap for its congressional districts was the worst in the country during the 2016 election, according to the League of Women Voters’ opening statement, saying the GOP won more seats than they should have compared to its share of the statewide vote. They’ll offer a mathematician and a political scientist as expert witnesses at trial.

The GOP lawyers wrote these and other calculations are based on “flawed social ‘science'” and that the 2016 congressional map followed traditional redistricting guidelines better than any congressional map in state history.

Last month, the three-judge panel declined to delay the North Carolina case until after the U.S. Supreme Court’s ruling in the Wisconsin case, saying there were legal and factual differences.