President Barack Obama's reelection campaign has sued Ohio over a law restricting early voting, arguing that the law discourages some Ohioans from being able to cast ballots.

Democrats have been warning for months that a spate of new voting laws imposing new identification requirements, tightening registration rules and curtailing early voting -- nearly all of them passed by Republican legislatures and signed by Republican governors -- could skew the election. The Democratic National Committee vowed to counteract what its chair called an assault on voting rights, and Attorney General Eric Holder has emerged as an outspoken critic of the new laws, recently likening a Texas voter ID law to a poll tax.

Holder's Justice Department has sued to block implementation of several of those laws, but the Ohio lawsuit marks the first time president's reelection campaign has joined the fray. Under the Ohio law, military personnel and overseas voters are allowed to vote through the Monday preceding the election, which falls on a Tuesday, while others are prohibited from early in-person voting after the Friday before the election.

The Obama campaign argued that the new law violates the Constitution's equal protection clause by extending early voting rights to only some voters.

This lawsuit seeks to treat all Ohio citizens equally under the law, Bob Bauer, the attorney for Obama for America, the president's campaign committee, said in a conference call with reporters. We want to restore the right of all to vote before Election Day. 

Driving the dispute is Ohio's role as a crucial swing state. Nearly a third of Ohioans voted before election day in 2008, when Obama won the perennial battleground en route to the presidency. The implications of a law restricting early voting in 2012 are not lost on the Obama campaign.

Without early voting in these last three days before Election Day, tens of thousands of citizens who would have otherwise exercised their right to vote during this time period, including the plaintiffs' members and supporters, may not be able to participate in future elections at all, the campaign's complaint says.

Ohio Counties had been able to set their own hours for early in-person voting, but the new law establishes a statewide standard. Ohio Secretary of State Jon Husted, who oversees elections and is named in the lawsuit, rejected the Obama campaign's argument that the law creates inequality, saying it instead established uniform rules.

I didn't see a lawsuit occur when six counties had weekend voting and extended hours and 82 of them didn't, Husted told the Associated Press. I'm sympathetic to the idea that we should have consistency, because that's exactly what we've been doing on a number of fronts.

The Democratic National Committee and the Ohio Democratic Party joined the Obama campaign in filing the lawsuit, and Ohio Democratic Party Chairman Chris Redfern said the party would be vigilant in trying to counteract the new law with a get-out-the-vote campaign.

It's a chilling notion that someone would be opposed to allowing early voting because of how a person may or may not vote, Redfern said.