A federal judge ruled on Tuesday that Ohio violated voters' rights in 2014 by cutting the number of days in which people were allowed to cast early ballots to 28 from 35.
Judge Michael Watson of U.S. District Court in Columbus ordered Ohio to reinstate the 35-day period and also to grant residents a week-long opportunity to register and cast a ballot at the same time - a period known as "Golden Week."
If the ruling stands, voters in Ohio will be able to vote a full 35 days before the general election on Nov. 8.
Watson said the earlier changes violated the Voting Rights Act of 1965 and were unconstitutional.
Ohio's Republican-controlled legislature changed the system two years ago. The move was challenged by the state's chapter of the National Association for the Advancement of Colored People and the American Civil Liberties Union.
The two groups argued that the limited opportunities for early voting directly affected minorities.
Ohio Secretary of State Jon Husted, a Republican, said in a statement on Tuesday: "It is disappointing that a federal judge would again change the election rules after the current laws were upheld in the same federal district court by a settlement agreement we reached with the NAACP and the ACLU." Husted said in a statement.
The settlement between Husted and the organizations allowed residents to vote on multiple Sundays leading up to a presidential election and gave access to additional evening voting hours, according to ACLU documents.
Husted said he plans to consult the leaders of the state Senate and state House of Representatives before deciding how to proceed.
(Reporting by Gina Cherelus in New York; Editing by Matthew Lewis)