The Internal Revenue Service is preparing to give a team member working with Elon Musk’s so-called Department of Government Efficiency access to sensitive taxpayer data, people familiar with the matter said.

The systems at the I.R.S. contain the private financial data tied to millions of Americans, including their tax returns, Social Security numbers, addresses, banking details and employment information.

“Waste, fraud and abuse have been deeply entrenched in our broken system for far too long,” Harrison Fields, a White House spokesman, said. “It takes direct access to the system to identify and fix it.”

Mr. Fields added: “DOGE will continue to shine a light on the fraud they uncover as the American people deserve to know what their government has been spending their hard-earned tax dollars on.”

The examination of the I.R.S. system represents the latest move by members of Mr. Musk’s team to push the boundaries of access to government data beyond what is typical for political appointees. The Treasury Department has faced questions in recent weeks after lieutenants of Mr. Musk who were assigned to the agency started scrutinizing the Bureau of the Fiscal Service’s system, which directs payments across the federal government.

Gavin Kliger, a young software engineer who was brought into the Office of Personnel Management as part of the DOGE effort, worked at I.R.S. headquarters on Thursday, according to two people familiar with the matter who were not authorized to speak publicly. He will be assigned to the I.R.S. as a senior adviser to the acting commissioner. The tax agency is still working out the exact terms of his work at the I.R.S., though he is expected to have broad access to its systems, according to the two people.