The U.S. Justice Department has sent a letter to Elon Musk's super PAC warning that the billionaire Tesla CEO's $1 million giveaways may violate federal law, several media organizations reported on Wednesday, citing people briefed on the matter.

A letter from the department's public integrity section, which investigates potential election-related law violations, went to the PAC.

The Justice Department and Musk's America PAC did not immediately respond to a request for comment.

South African-born Musk, who has thrown his support behind Republican presidential candidate Donald Trump ahead of the November 5 election, announced on Saturday while speaking before a crowd in Pennsylvania that he was giving away $1 million each day until Election Day to someone who signs his online petition supporting the U.S. Constitution.

He handed $1 million checks to two separate people over the weekend — one to a man in Harrisburg on Saturday and another to a woman in Pittsburgh on Sunday.

Musk, ranked by Forbes as the world's richest person, so far has supplied at least $75 million to America PAC, according to federal disclosures, making the group a crucial part of Trump's bid to regain the White House.