Leading Democrats on Monday demanded an investigation of possible criminal corruption involving Elon Musk, the tech billionaire and world’s richest man tasked by Donald Trump with slashing the federal government.

The investigation should involve “the Federal Aviation Administration’s decision to cancel a $2.4bn contract with Verizon to upgrade air traffic control communications, and to pay … Musk’s Starlink to help manage US airspace”, senators Chris Van Hollen, Richard Blumenthal and Elizabeth Warren wrote to Pam Bondi, the attorney general, and Mitch Behm, acting inspector general of the transportation department.

“We ask that the Department of Transportation’s Office of Inspector General and the Department of Justice investigate the scope of Mr Musk’s activities at the FAA,” the senators said.

An investigation, the letter said, would determine whether Musk, “in his capacity as a special government employee in the White House … has participated in any particular matter in which he has a financial interest, which would violate the criminal conflict-of-interest statute”.

Sent amid widespread concern over the state of the US air traffic control system under Trump, after a string of crashes and accidents, some fatal, the letter and two others were provided exclusively to the Guardian.

In a lengthy letter to Susie Wiles, Trump’s White House chief of staff, the three senators were joined by Jeff Merkley of Oregon and the Maryland congressman Jamie Raskin in citing powers of congressional oversight when they asked to “provide written assurances that [the administration] will immediately remediate the worst” instances of a long list of alleged conflicts of interest and corruption arising from Trump’s first two months in power.

A third letter asked Gene Dodaro, the comptroller general, to mount a Government Accountability Office investigation into whether the appointment of former Georgia congressman Doug Collins to run both the US Department of Veterans Affairs and the Office of Government Ethics is undermining either body.

Musk’s vast wealth has been attained through companies including Tesla, X and SpaceX, which makes Starlink satellite internet technology. Having donated hundreds of millions to Trump’s election campaign, he has taken charge of the so-called “department of government efficiency” or Doge, an effort to slash federal budgets and staffing.

Addressing Bondi and Behm, the Democrats said that as a special government employee, Musk should be “subject to federal conflict-of-interest rules” and “may be using his government role to benefit his own private company”.

Citing the Washington Post, Bloomberg News, and Rolling Stone, the Democrats said: “Reports indicate that some personnel of SpaceX, Starlink’s parent company, have already begun working at the FAA.

“Additionally, Starlink has begun shipping its hardware to the FAA, though the company has stated that it is providing satellite kits to the agency free of charge. However, sources suggest that the FAA is ordering staff to ‘begin finding tens of millions of dollars for a Starlink deal.’”

SpaceX has called reports about its FAA dealings “false”, adding: “Starlink is a possible partial fix to an aging system. There is no effort or intent for Starlink to ‘take over’ any existing contract – that’s just FUD”, meaning “fear, uncertainty, and doubt”.

In February, in a joint Oval Office appearance with Trump, Musk said: “All of our actions are fully public. So, if you see anything you say like, wait a second, hey, you know what … that seems like maybe that’s, you know, that there’s a conflict there, it’s not like people are going to be shy about saying that. They’ll say it immediately.”

Trump said that if he thought Musk might have a conflict, “we would not let him do that segment or look in that area”.

Allegations of corruption and conflicts of interest involving Trump are legion, ever since he entered politics in 2015.

In their letter to Wiles, the Democrats said: “Despite President Trump’s promises to fight for working families, he has appointed a string of corporate billionaires and industry insiders, putting them in positions to enrich themselves at the expense of ordinary Americans.”

Last week, Trump used the White House lawn to attempt to drive customers to a Musk business, Tesla, which has seen its share price slump amid unease over Musk’s cost-cutting and outrage over behavior including giving Nazi-style salutes and abusing US allies.

Calling Musk Trump’s “unelected ‘co-president’”, the Democrats accused him of “relentlessly attacking and disarming federal agencies that regulate his companies, even as his companies have benefited from billions in federal contracts”.

Saying “corruption scandals were a feature of President Trump’s first term”, the Democrats listed potential scandals in the second, including appointing lobbyists to roles overseeing their own industries and allowing other appointees to give investments in their own sectors to their adult children.”

Instances cited included Trump boosting his own social media platform and ventures in cryptocurrency; continuing to seek expand his foreign and domestic real estate holdings, including an attempt to buy back the former Trump Hotel on Pennsylvania Avenue; and using his Mar-a-Lago home in Florida as “a well-oiled pay-to-play machine”.

The Democrats noted Trump’s firing of the director of the Office of Government Ethics, a first in US history, and his dismissal of “at least 17 inspectors general”, independent department watchdogs, without notifying Congress as required; and his attempt to fire the head of the Office of Special Counsel.

But despite it all, the Democrats said, Trump’s decision to “cede power” to Musk remained his most concerning move.

“Since President Trump took office,” the Democrats told Wiles, “at least 11 … agencies with ‘investigations, pending complaints or enforcement actions’ against Musk’s companies have been hamstrung, including through the firing of the agencies’ independent commissioners and rolling back the agencies’ independence.

“Meanwhile, Musk’s companies – which have already received at least $38bn in federal funding – are vying for new federal contracts.”

The letter also raised a mooted purchase of Tesla vehicles by the state department and Musk’s attempt to buy OpenAI while “insisting that agencies increase their reliance on artificial intelligence”.

“Musk has done all of this without so much as disclosing his financial interests to the public,” the Democrats said.

The Democrats said Trump could still take steps “to reverse course and put our national interests ahead of his personal dealings”. Such steps included reinstating fired watchdogs, vetting nominees for conflicts of interest, and revoking Musk’s “power to profit from his efforts to manipulate the executive branch for his own benefit”, while being required “to promptly release his financial disclosure form so that the public can understand his potential conflicts of interest”.

Setting a deadline of 31 March, the Democrats asked Wiles to answer six questions.

Will Trump, they asked, reinstate “all government watchdogs he has purportedly fired and … protect their independence from political interference”; commit not to “appoint additional officials [with] direct conflicts of interest that cannot be resolved … under existing ethics law”; “issue an ethics pledge” for new nominees; “commit to divest from his private business interests, as every prior president in the modern era has done”; “commit to disclose his tax returns from the past three years”; and require Musk “to publicly release his financial disclosure form”?

Trump, Musk and Wiles did not immediately comment.