The Department of Government Efficiency, run by President Donald Trump’s billionaire adviser and Tesla CEO Elon Musk, has gained access to sensitive Treasury data including Social Security and Medicare customer payment systems.

A senior U.S. lawmaker says representatives of Elon Musk were granted “full access” to a U.S. Treasury payments system used to disperse trillions of dollars to Americans each year, and warned that Musk’s access to the system poses a “national security risk.”