Washington DC - Elon Musk and his aides have taken control of the US Treasury Department's payments system, triggering a lawsuit charging he is illegally getting access to private data of millions of Americans.

Musk, the world's richest person, is leading President Donald Trump's federal cost-cutting efforts under the so-called Department of Government Efficiency (DOGE).

The suit calls on a federal judge to declare it illegal for Musk or others from DOGE to get personal information about taxpayers and to block the Treasury Department from letting that happen.

"People who must share information with the federal government should not be forced to share information with Elon Musk or his 'DOGE,'" read a lawsuit filed in Washington by labor unions and a grassroots advocacy group. "And federal law says they do not have to."

Taylor Swift Taylor Swift Super Bowl parties: How to celebrate the big game, Swiftie style!

Musk said Monday in a post on X, the social media platform he owns, that the "only way to stop fraud and waste of taxpayer money is to follow the payment flows and pause suspicious transactions for review."

"Naturally, this causes those who have been aiding, abetting, and receiving fraudulent payments to become very upset. Too bad," he added.

The Treasury's closely guarded payments system handles the money flow of the US government, including $6 trillion annually for Social Security, Medicare, federal salaries, and other critical payments.

Musk's control of the payments system was approved by incoming Treasury Secretary Scott Bessent and was made possible when a career official was put on administrative leave Friday after refusing to hand over access, according to the lawsuit.

The official subsequently retired from the department, a source close to the matter told AFP and the lawsuit confirmed.

Kanye West Were Kanye West and Bianca Censori kicked out of Grammys over NSFW look?

Bessent's granting access of personal Treasury information to DOGE-affiliated individuals means "individuals from all walks of life have no assurance that their information will receive the protection that federal law affords," the lawsuit argued.

Wired magazine reported that Musk has placed young surrogates working for DOGE into key government positions, with his team gaining unprecedented access to the payment systems typically restricted to career employees.

The staff members, reportedly aged between 19 and 24, were also placed at the federal Office of Personnel Management, the human resources department for federal workers.

Last week, the office sent an email offering most employees the option to leave government service immediately with approximately nine months' severance pay, though many legal experts warned staff to be wary of the offer.

Trump on Sunday praised Musk as "a big cost-cutter."

"Sometimes we won't agree with it and we'll not go where he wants to go. But I think he's doing a great job," the president said.

Democratic lawmakers are expressing deep concerns about political operators having access to the US government's money flow, saying it amounts to an illegal power grab.

"They are seizing the tools you need for a coup," said Senator Ron Wyden, the top Democrat on the Senate Finance Committee.

Elizabeth Warren, the ranking Democrat on the Senate Banking Committee, blasted the move as "extraordinarily dangerous" and said it posed a systemic risk to the economy.

"I am alarmed that as one of your first acts as secretary, you appear to have handed over a highly sensitive system responsible for millions of Americans' private data – and a key function of government – to an unelected billionaire and an unknown number of his unqualified flunkies," Warren wrote in a letter to Bessent.

She also said sidelining experienced staff in this crucial corner of government "puts the country at greater risk of defaulting on our debt, which could trigger a global financial crisis."

On X, Musk predicted "Excitement guaranteed" in response to a post that said DOGE would uncover an "unprecedented amount of fraud and corruption in numerous government departments."