An Ohio county must allow new voters to register and cast an absentee ballot on the same day during a weeklong period that begins Tuesday, a federal judge ruled Monday.

U.S. District Judge James Gwin in Cleveland issued a temporary restraining order forcing Madison County to follow Secretary of State Jennifer Brunner's instructions. The county had said that, one the advice of its county prosecutor, it was not going to allow same-day voting during the six-day window that runs through Oct. 6.

It was the first of three court decisions involving an early voting window that has become a highly partisan battle.

Both Democratic presidential candidate Barack Obama's campaign and the Republican National Committee have urged supporters in Ohio to use the early voting. But there are Republican-backed lawsuits against it.

The state GOP has filed a statewide challenge to the voting window in federal court in Columbus. A hearing was scheduled for Monday.

Two GOP-backed voters also have filed a lawsuit in the Ohio Supreme Court, which could rule Monday.

The two lawsuits argue that Ohio law requires voters to be registered for at least 30 days before they cast an absentee ballot. Republicans have said Ohio law doesn't allow same-day registration and voting, and have accused Brunner, a Democrat, of reading a partisan interpretation into law to benefit her own party.

The disputed voting window results from an overlap between Tuesday's beginning of absentee voting 35 days before Election Day, and the Oct. 6 end of voter registration period.