A three-judge federal panel ruled Thursday that Michigan's congressional and legislative maps were unconstitutionally gerrymandered for partisan gain, ordering the state Legislature to redraw at least 34 districts for the 2020 election.

The decision also requires special state Senate elections to be held in 2020, instead of 2022 as scheduled. It is the latest development in a series of redistricting lawsuits in at least a dozen states.

The judges said 34 of the 162 congressional and legislative districts drawn by Republicans in 2011 violate Democratic voters' constitutional rights, including by diluting the weight of their votes. They gave the GOP-led Legislature until Aug. 1 to submit new maps, which would need the signature of Democratic Gov. Gretchen Whitmer. An appeal is likely.

Get Breaking News Delivered to Your Inbox

The federal panel - Judge Eric Clay of the 6th U.S. Circuit Court of Appeals, U.S. District Judge Denise Page Hood of Michigan's eastern district and U.S. District Judge Gordon Quist of Michigan's western district - said those involved in the 2011 redistricting effort elevated "partisan considerations" at every step.

"Their primary goal was to draw maps that advantaged Republicans, disadvantaged Democrats, and ensured that Republicans could enjoy durable majorities in Michigan's congressional delegation and in both chambers of the Michigan legislature for the entire decade," the judges wrote.

The ruling came in a lawsuit filed by the League of Women Voters of Michigan and Democratic voters who claimed districts were shaped by Republican operatives to guarantee the party's dominance in the state Capitol after the 2010 census. They said constitutional rights were violated when Democratic areas were packed in certain districts or diluted elsewhere.

The panel of judges held a trial after rejecting newly elected Democratic Secretary of State Jocelyn Benson's attempt to settle the suit by redrawing at least 11 state House districts for the 2020 election.

GOP lawmakers who intervened in the suit have said the entire proceeding should be halted until the U.S. Supreme Court rules on redistricting cases from North Carolina and Maryland. In oral arguments last month, conservative justices who hold a 5-4 majority seemed wary of getting federal judges involved in determining when electoral district maps are too partisan.