Ohio implemented early-voting after the 2004 election fiasco where huge lines formed at polling stations and countless voters gave up and went home.

But the Republican-led Ohio legislature changed the rules last year so that only members of the military could cast in-person ballots after 6 pm on the Friday before the election.

Ohio Secretary of State Jon Husted also ordered local polling stations to only operate during normal business hours, thus preventing early voting in the evenings and weekends.

He argued the rules were necessary in order to help poll workers prepare for the November 6 election.

The Obama campaign challenged the rules in court, arguing that allowing members of the military but not the general public to vote on the weekend before election day violated constitutional guarantees to equal treatment.

A federal appeals court found in Obama's favor and the Supreme Court denied Husted's appeal in a single sentence: "The application for stay presented to Justice Kagan and by her referred to the Court is denied."

Early voting has been a boon for Democrats in Ohio, whose mobilization efforts included bussing supporters to the polls after church on the Sunday before the election.

The Obama campaign hailed the Supreme Court's decision as a "victory for voting rights."

"This action from the highest court in the land marks the end of the road in our fight to ensure open voting this year for all Ohioans, including military, veterans, and overseas voters," General Counsel Bob Bauer said in a statement.

Husted did not immediately respond to the court's ruling.

He has called the ruling "federal overreach" into state election law and was joined by election officials from 15 states in urging the Supreme Court to overturn the ruling.

"If allowed to stand, the precedent set by this decision in the state of Ohio will have far reaching consequences for all 50, whether they are 'red,' 'blue,' or 'swing' states," Husted said in a statement Friday.

Early voters tend to include older citizens, women, and people of lower income and education attainment who may have a hard time making it to the polling station on a Tuesday. These groups also tend to vote for Democrats.

Some 30 percent of ballots cast in the 2008 election in Ohio were early votes.