If you're a U.S. citizen over the age of 18, you have the right to vote.

If you're convicted of a felony, you could have that right taken away — but it all depends on where you live.

In Kentucky, you'll lose the right to vote forever. In Wisconsin, you'll only get it back after you've finished probation and parole. In Vermont, you can mail your ballot from prison.

Civil-rights groups are pushing back against some of the tighter restrictions with lawsuits, most recently with a successful case in Washington state.

Meanwhile, the mishmash of state laws has led some to call for new federal standards which would allow felons to vote once they've left prison. Companion bills in the House and Senate (HR 3335 and S 1516), for instance, would require all states to give ex-felons the right to vote in federal elections.

But advocates admit that they face an uphill battle: few politicians want to go on record defending the rights of felons, and polls show many Americans support restrictions.

"I'd be surprised if it were able to pass this year," said Marc Mauer, the executive director of the Sentencing Project in Washington, D.C., of the proposed legislation. "It's one of those issues that could take several years to build up broad bipartisan support."

Laws that prevent felons from casting ballots are centuries old.  The practice came to America by way of the British colonies, which in turn were following a precedent set by the ancient Greeks and Romans.  They bestowed upon criminals "civil death," a banishment from the political community.

Virginia was the first state to pass a law prohibiting ex-felons from voting and, by 1869, 28 states had followed suit. Today, 48 states have some kind of barrier in place.