In an effort to restore three days of early voting in a key swing state, the Obama campaign filed a federal lawsuit Tuesday against Ohio Secretary of State Jon Husted that alleges that new GOP-backed state laws violate the U.S. Constitution by giving some voters an advantage over others.

The complaint, filed in U.S. District Court in Columbus, says that members of the military, their spouses and dependents may vote early by casting ballots in-person in their home counties through the Monday before Election Day. However, in-person early voting ends for everyone else at 6 p.m. on the Friday before.

This violates the equal protection clause of the Constitution, said Don McTigue, attorney for the Ohio Democratic Party.

Husted said federal law sets different standards for military voters, such as allowing them to begin early voting 45 days before Election Day instead of 35 days or allowing them to receive absentee ballots electronically rather than by mail. The in-person early voting standard for military personnel is established by federal law, Husted said.

“We don’t have any discretion in the matter,” he said. Husted added that he supports having uniform voting rules for all Ohio voters.

After long lines at the polls for the 2004 presidential election, Ohio expanded absentee and in-person voting. Early voting has proven popular. In 2008, roughly 30 percent of ballots in Ohio were cast early, and 93,000 Ohioans voted during the three days leading up to Election Day, according to the Democrats. Husted said he expects a greater percentage of voters to vote absentee this year because every registered voter will receive an absentee ballot application in the mail just after Labor Day.

The Obama lawsuit is the latest salvo in a bitter partisan battle over Ohio’s voting laws.

Citing concerns about potential voter fraud and voting rules that varied by county, the GOP-controlled General Assembly in 2011 passed House Bill 194, which collapsed the early voting window to the equivalent of 11 days, down from 35 days, and eliminated in-person early voting the three days before Election Day.

Voting rights advocates, Democrats and unions then turned in more than 300,000 petition signatures to force a referendum on House Bill 194 this fall. In the interim, state lawmakers passed another law dealing with military voting.

A Dayton Daily News analysis of 2008 in-person early voting patterns in five counties showed that Democrats were much more likely than Republicans to vote early, especially in urban counties. The analysis suggested Democrats would be more impacted by the GOP-led initiative than Republicans.

In May, lawmakers repealed House Bill 194, thus removing the need for a referendum. However, the repeal did not restore early voting in the final three days because those were taken away in a separate bill. The net result is two different deadlines and two different classes of voters, the Democrats argue.

Ohio Democratic Party Chairman Chris Redfern dismissed the idea that his party is suing because early voting tends to help Democratic candidates. Each side has the opportunity to get their voters to the polls on those days, he said.

The lawsuit is brought by Obama for America, the Democratic National Committee and the Ohio Democratic Party. The case will go before U.S. District Judge Peter Economus, who was appointed to the federal bench in 1995 by President Bill Clinton.

The Democrats are seeking a preliminary injunction to allow for early in-person voting for everyone through the Monday before Election Day.