The Philadelphia district attorney sued Elon Musk and his super PAC on Monday over the billionaire's controversial $1 million registered voter giveaway.

The lawsuit from Philadelphia District Attorney Larry Krasner claims Musk and his America PAC are "running an illegal lottery in Philadelphia (as well as throughout Pennsylvania)."

Musk announced the eighth winner of his super PAC's $1 million prize in Lancaster, Pennsylvania, on Saturday and doubled down on his promise to continue offering the money to a registered swing state voter who has signed his petition. He said participants are not required to vote, but the online petition form says one has to be a registered voter to be eligible.

"We're trying to get attention for this very important petition to support the Constitution. And, it's like, if we, you know -- we need the right to free speech; we need the right to bear arms," Musk said at the rally.

"So we're going to be giving out a million dollars every day through Nov. 5," he continued. "And also, all you have to do is sign the petition in support of the First and Second Amendment. That's it. You don't even have to vote. It'd be nice if you voted, but you don't have to. And then just basically sign something you already believe in, and you get a test to win a million dollars every day from now through the election."

This is a developing story. Please check back for updates.