Lansing — A lawsuit alleging partisan gerrymandering by Michigan's Republican-led Legislature is heading toward trial next week after a three-judge panel rejected a settlement proposed by Democratic Secretary of State Jocelyn Benson and plaintiffs.

Benson does not have the authority to enter into the proposed consent decree without the blessing of the Michigan Legislature, the federal judges said Friday in a ruling rejecting the deal, which would have required reconfiguration of at least 11 state House seats for 2020 elections.

A trial in the high-stakes case is set to start Tuesday, but the U.S. Supreme Court could still intervene. GOP attorneys are attempting to delay the case, and Justice Sonia Sotomayor on Friday asked parties wishing to weigh in to do so by Monday at 11 a.m., a sign the High Court is considering the request.

The suit was filed on behalf of the League of Women Voters and a series of Democrats who allege that congressional and legislative district boundaries approved by the Legislature in 2011 were designed to benefit Republican candidates.

In announcing plans to settle, Benson said the case included "significant evidence of partisan gerrymandering" and predicted the state would lose in court and incur significant legal costs. Her settlement focused on what she said were the most "egregious" examples of partisan gerrymandering -- and likely several neighboring districts as well.

Instead, the court could decide whether there is evidence to prove claims Republicans intentionally "packed" and "cracked" voters into certain districts.

Benson and plaintiffs had argued their proposed settlement was similar to a case out of Florida that the U.S. Supreme Court approved.

But in that case, the Florida Senate and House "explicitly consented to the relief contained in the consent decree," Sixth Circuit Court of Appeals Judge Eric Clay wrote on behalf of the panel, which includes District Court judges Denise Page Hood and Gordon Quist.

Attorneys for GOP state House Speaker Lee Chatfield, Rep. Aaron Miller and several congressional Republicans had filed motions opposing the settlement. The court on Friday also granted a motion for the Republican-led state Senate to intervene in the case.

Clay rejected arguments from Benson and plaintiffs that they could enter into a settlement because of a Michigan Supreme Court ruling giving the Attorney General's office broad authority to sue and settle state litigation with "binding effect on Michigan's political subdivisions."

The proposed settlement "would invalidate maps approved and enacted by the Michigan Legislature," Clay wrote. "And the Michigan Constitution gives the Michigan Legislature, not any political subdivision, authority to 'enact laws to regulate the time, place and manner of all... elections.'"

An attorney for the plaintiffs was not available, but Benson said she respects the court's decision.

"As the state’s chief election officer, I will continue efforts to resolve this lawsuit in the best interests of all voters and in compliance with constitutional requirements," Benson said in a statement.

Michigan Republicans have denied overt political bias in the district maps, but emails between map makers revealed as part of the federal case have included several partisan references and commentary on the prospects of maintaining GOP power.

Former Secretary of State Ruth Johnson, a Republican, had defended the 2011 maps, but Benson inherited the case after taking office Jan. 1 and quickly reversed course. While the settlement would have been limited in scope, the lawsuit challenges 34 congressional, state House and Senate districts.

Republican attorneys had asked to delay the trial pending the outcome of alleged gerrymandering cases from Maryland and North Carolina the Supreme Court is set to take up, with oral arguments in late March.

The three-judge panel also denied those requests, saying all parties to the case "failed to articulate sufficiently compelling justifications" for delaying the trial, but the Supreme Court is weighing a similar request.

Michigan voters in November approved creation of an independent redistricting commission that will draw new political boundaries for 2022 elections and beyond. State law had allowed the Legislature to control that process every 10 years.

joosting@detroitnews.com