Civil rights advocates filed suit against the law, passed in February, which eliminated the "Golden Week" voting period where voters could register and cast a ballot on the same day. They also challenged a directive from the state Secretary of State Jon Husted, to cut Sunday and evening early voting hours.
"Ohio and Secretary Husted may not capriciously change or implement that system in a manner that disproportionately burdens the right to vote of certain groups of voters," Judge Peter Economus of the Federal District Court wrote in his ruling.
Under Economus' order, early voting will begin September 30, instead of October 7. He also ordered Husted to expand evening hours and add another Sunday to the schedule.
Proponents of the changes said their goal was to distinguish between periods for registration and for voting. But plaintiffs, including the Ohio chapters of the American Civil Liberties Union and the National Association for the Advancement of Colored People, said the cuts were discriminatory, since they particularly impacted minority voters.
Blacks in Cayahoga County, the state's most populous, cast 56 percent of the county's early votes in 2008, even thought they made up just 28 percent of the population. And in 2012, more than 157,000 people voted on days that were due to be eliminated in 2014.
"Today's ruling kicks the door open to having different rules for voting in each of Ohio's 88 counties, which is not fair and uniform and was not even acceptable to this court or the plaintiffs previously," Husted said, adding the state would appeal the ruling.