Washington DC - The US Treasury said Tuesday that Elon Musk's government reform team can read data from its highly sensitive payment system but not alter it, after Democratic lawmakers raised the alarm over the move and called for an investigation.

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).

As part of that drive, he reportedly pushed for a team led by IT executive Tom Krause to be given access to the Treasury Department's closely guarded payment system, which handles trillions of dollars of transactions, from Social Security and Medicare payouts to federal salaries.

In response, Democratic Senators Elizabeth Warren and Ron Wyden sent a letter Tuesday to the congressional watchdog agency demanding it probe reports that Treasury Secretary Scott Bessent had personally granted Musk and his aides – who are reportedly young and inexperienced – that permission.

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The Treasury, in a letter sent to Congress and shared with AFP, confirmed Krause's team has access to the system, but said it is "read-only access... in order to continue this operational efficiency assessment."

They said the permission was "similar to the kind of access that Treasury provides to individuals reviewing Treasury systems, such as auditors."

Musk's increased power over large swathes of government institutions has run into strong opposition from Democratic lawmakers, who have raised a wide range of legal and ethical concerns about his moves to slash federal spending.

In a separate letter sent to Republican President Donald Trump on Tuesday, other Democratic policymakers expressed concern over DOGE's work involving government data and facilities.

Labor unions and a grassroots advocacy group have also objected to the moves, filing a lawsuit calling on a federal judge to declare it illegal for Musk or others from DOGE to get personal information on taxpayers, and to block the Treasury Department from letting that happen.

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

Musk's access to the payments system was approved by Bessent and made possible when a career official was put on administrative leave after refusing to allow entry, according to the lawsuit. The official later retired.