Elon Musk's pro-Trump PAC could face legal consequences for its $1 million voter contest, according to a warning from the DOJ.

• The super PAC founded by Elon Musk, which is pro-Trump and spends $1 million per day on voter outreach, may be in violation of federal election law, according to a warning from the DOJ, as reported by NBC News.
• Federal law bars paying people to vote or to register to vote.
• Elon Musk, CEO of Tesla and SpaceX, declared that he would award $1 million daily to registered voters in Pennsylvania, Georgia, Nevada, Arizona, Michigan, Wisconsin, and North Carolina who sign his PAC's petition.

On Wednesday, a source close to the matter revealed to NBC News that the Department of Justice had issued a warning to the Elon Musk-founded super PAC about its $1 million-per-day voter sweepstakes, which may be in violation of federal election law.

The DOJ's Public Integrity Section sent a letter to America PAC, a group backed by Musk to support Republican presidential candidate Trump, raising concerns about the legality of a large donation.

On Saturday, Musk, CEO of both Tesla and SpaceX, declared that he would award $1 million daily to a randomly chosen registered voter in seven crucial swing states upon signing his PAC's petition.

The most competitive battlegrounds in the contest between Trump and Democratic nominee Kamala Harris are Pennsylvania, Georgia, Nevada, Arizona, Michigan, Wisconsin, and North Carolina.

It is illegal under federal law to pay individuals to vote or register to vote. While the petition does not require signers to disclose their political affiliation, it does request personal information such as an email address and phone number.

Earlier Wednesday, CNN and 24Sight News reported that the DOJ sent a letter, but it was unclear when exactly it was sent. When asked for comment, a DOJ spokesman declined CNBC's request.

Chris Gober, the lawyer for America PAC, did not promptly reply when contacted by CNBC regarding a reported letter.

Musk, the world's wealthiest man, has been a significant supporter of Trump's White House campaign, with America PAC spending over $100 million on the election, most of which was funded by Musk himself.

— CNBC's Lora Kolodny contributed reporting.