President Obama's re-election campaign has filed suit in federal court to block a Republican-sponsored Ohio law that mandates an end to early, in-person voting a full three days before Election Day this fall.

The lawsuit is the latest twist in an ongoing battle over early voting in the state between Obama allies and the Republican-controlled Ohio legislature and Gov. John Kasich.

Democrats say the Saturday, Sunday and Monday before Nov. 6 are critical days to "bank votes" needed to win Ohio. In 2008, 30 percent of the total vote came during early voting, including an estimated 93,000 votes during the last three days, according to a nonpartisan voter advocacy group.

Republicans say the early vote process is too long, too costly for budget-strapped counties and too prone to fraud and abuse. They also insist trimming the voting period - not eliminating it entirely - does not upend the convenience of the current process.

Before the law, local election boards could decide at their own discretion whether or not to hold early, in-person voting during the last three days.

"The last three days of Early Vote are especially important to ensuring a free and fair election," Obama's Ohio campaign said in a statement. "We are moving forward in the fight to reinstate the last 3 days of Early Voting and ensure that all Ohio voters can make their voices heard this November."

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