(CNN) - Mitt Romney lashed out Saturday against President Barack Obama's campaign and Democratic allies, who sued Ohio requesting the state’s early voting law apply equally to all voters, rather than only to military personnel and citizens who reside overseas.
Romney issued a statement calling the lawsuit an "outrage," and claimed the Democrats' lawsuit argues "it is unconstitutional for Ohio to allow servicemen and women extended early voting privileges during the state's early voting period."
But the lawsuit argues the additional three days of early voting afforded to military personnel and citizens who reside overseas should be opened to all voters. Obama's campaign on Saturday said Romney's criticism was "shameful" and based on a "fabricated" claim.
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The lawsuit involves a series of state laws that Democrats say will lead to "disparate treatment" in access to in-person early voting, according to a court document. It was filed on July 17 by Obama's campaign, the Democratic National Committee, and the Ohio Democratic Party against the state's attorney general and secretary of state. The laws were passed by the Republican-led legislature and signed by the GOP governor, John Kasich.
At stake is the cutoff for pre-Election Day in-person early voting, which the state introduced after long lines and other issues plagued the state in the 2004 election. Under the new Ohio laws, registered voters who fall under the federal Uniformed and Overseas Citizens Absentee Voter Act may vote early, in person, through the day before Election Day, which is a Tuesday. But the last day for those who don't meet those criteria to vote in person is the Friday before Election Day - giving UOCAVA-eligible voters access to the polls on three days when others may not vote.
Many UOCAVA-eligible voters are members of the military, as the 1986 federal law covers "members of the United States Uniformed Services and merchant marine; their family members; and United States citizens residing outside the United States," according to the U.S. Justice Department.
The Democrats' lawsuit asks the court to find that the Friday deadline for non-UOCAVA voters violates the Constitution's Equal Protection Clause, and to restore "in-person early voting on the three days immediately preceding Election Day for all eligible Ohio voters."
The lawsuit acknowledges the disparity involved "legislative confusion," but says, "at worst, the differential treatment has been influenced by partisan politics." Those who had served in the military voted 54% for Sen. John McCain and 44% for Obama in the 2008 election, according to CNN national exit polling data.
In a statement, Romney said: "The brave men and women of our military make tremendous sacrifices to protect and defend our freedoms, and we should do everything we can to protect their fundamental right to vote. I stand with the fifteen military groups that are defending the rights of military voters, and if I'm entrusted to be the commander-in-chief, I'll work to protect the voting rights of our military, not undermine them."
A representative of Obama's campaign - Obama for America Veterans and Military Family Vote Director Rob Diamond - responded with a statement on Saturday.
"Mitt Romney and his campaign have completely fabricated a claim that the Obama campaign is trying to restrict military voting in Ohio," Diamond said. "In fact, the opposite is true: the Obama campaign filed a lawsuit to make sure every Ohioan, including military members and their families, has early voting rights over the last weekend prior to the election. The case filed with the court could not be clearer on this point."
Among the groups supporting Ohio Secretary of State Jon Husted and Attorney General Mike DeWine - and siding with Romney's position - are the National Guard Association of the United States, the Association of the U.S. Army, Association of the U.S. Navy, Marine Corps League and Military Officers Association of America, according to court filings.
The groups filed with the court a motion to intervene, asking it to dismiss the case. As to the different voting provisions, the groups argued "it is both laudable and constitutionally appropriate for the State to do everything in its power to facilitate voting by military personnel in any form; the fact that similar arrangements are not offered to civilians does not render them unconstitutional."
The three additional days for UOCAVA-eligible voters meets the legal standard of having a "rational basis" and does not substantially burden others, the groups continued in their filing, as "the Ohio legislature reasonably could have concluded that military and overseas voters require special accommodation and flexibility in voting." Additionally, they contend the law does not discriminate based along the protected lines of "race, alienage, national origin, gender, [and] illegitimacy."
The suit says 29% of Ohio votes in 2008 were cast via absentee ballot, a number which included in-person early voting, and 93,000 voters cast ballots in the three days before Election Day.
The lawsuit was filed in U.S. District Court for the Southern District of Ohio, Eastern Division.
– CNN's Lindsey Knight contributed to this report