The group, an affiliate of the National Democratic Redistricting Committee, says the new map violates the new reforms placed in the Ohio Constitution by voters in 2018.
The map was signed into law over the weekend by Gov. Mike DeWine (R-Ohio).
It creates 12 districts that heavily favor or lean in favor of Republicans. That's 80% of the districts in a state that voted for Donald Trump with 53% of the vote.
The group says the map unduly splits counties and municipalities for "no discernible reason other than minimizing Democratic voting power."
For example, voters in overwhelmingly Democratic Cincinnati are carved out of the rest of Hamilton County and placed with voters in more conservative Warren County.
Republican leaders, including DeWine, said the map follows the constitution.