U.S. District Judges J.P. Stadtmueller of the Eastern District of Wisconsin, Diane Wood of the 7th Circuit Court of Appeals and Robert M. Dow Jr. of the Northern District of Illinois ruled that Assembly Districts 8 and 9 on Milwaukee's south side, as drawn by the GOP maps, violate the Voting Rights Act, and said the state Government Accountability Board (GAB) cannot implement the new maps in their current form.
Critics of the new maps had said the boundaries divided minority blocs and disenfranchised Latino voters.
A group of Democratic citizens and the immigrant rights group Voces de la Frontera filed lawsuits against the Milwaukee maps.
The court upheld all of the other legislative and congressional districts that Republicans drew last year that favor their party. Barring a counter-ruling by the U.S. Supreme Court, those GOP-friendly maps will be in place for the next decade, but they won't take effect until November.
Once every 10 years, states must draw new congressional and legislative districts to account for changes in population identified by the U.S. Census Bureau.
The judicial panel was critical of the secretive process the Republicans used in redrawing the maps.
"What could have - indeed should have - been accomplished publicly instead took place in private, in an all but shameful attempt to hide the redistricting process from public scrutiny," wrote the three-judge panel in a Feb. 16 order requiring the GOP turn over redistricting documents.
The court was critical of Republican legislators who agreed to sign a secrecy pledge to refrain from discussing the redistricting process in the public.