A group of Democratic senators is asking Defense Department and Air Force watchdogs to launch an investigation into tours that President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE has offered of Air Force One.

The letter to the inspectors general, dated Aug. 1 and released Thursday, comes weeks after BuzzFeed News reported that some members of Trump's private clubs in Florida appeared to have been invited for tours of the presidential plane.

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In the letter, Democratic Sens. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (Mass.), Tom Carper Thomas (Tom) Richard CarperThe conservative case for phasing out hydrofluorocarbons Democrat asks for probe of EPA's use of politically appointed lawyers Overnight Energy: Study links coronavirus mortality to air pollution exposure | Low-income, minority households pay more for utilities: report MORE (Del.), Richard Blumenthal (Conn.) and Sheldon Whitehouse Sheldon WhitehouseThe Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Feinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Hillicon Valley: Murky TikTok deal raises questions about China's role | Twitter investigating automated image previews over apparent algorithmic bias | House approves bill making hacking federal voting systems a crime MORE (R.I.) raise concerns about the potential overlap between Trump's role as president and his private business interests.

"Previous Presidents have provided friends and even campaign donors tours of Air Force One, but the reports that members of the President's private club may have received such tours are particularly troubling because their relationship to the President arises out of an ongoing business relationship with the President," the senators wrote.

The letter asks the inspectors general for a "review of all individuals who have had access to Air Force One for tours or other nonofficial travel" since Trump took office last year.

It also asks the internal watchdogs to make a determination as to whether any of the individuals who received tours of the aircraft had business relationships with Trump or his family and whether such relationships played a role in the decision to invite them aboard the plane.

Trump has faced scrutiny since taking office for his far-reaching business dealings, with critics and ethics watchdogs raising concerns that his business interests could conflict with his responsibilities as president.

As he prepared to take office last year, Trump passed off day-to-day control of his business empire to his two adult sons. But he also declined to put his assets in a blind trust and fully divest from his business.

BuzzFeed News obtained an invitation for the Air Force One tours that was sent to some members of Trump’s Florida clubs last year. That invitation was cross-checked with redacted records obtained by the news outlet through a Freedom of Information Act (FOIA) request.

Members reached by BuzzFeed neither confirmed nor denied whether they attended the tour of the presidential plane. But two tours were scheduled in February at the Atlantic Aviation FBO at Palm Beach International Airport.

Past presidents have given tours of Air Force One to family, friends and political donors.

Trump has brought guests aboard the aircraft in the past, including his adult sons Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE and Eric Trump Eric Frederick TrumpJudge orders Eric Trump to comply with New York AG's subpoena before Election Day Eric Trump uses misleading clip to blast Biden for using teleprompter Melania Trump: Ginsburg's 'spirit will live on in all she has inspired' MORE, neither of which works in his administration. In March 2017, Fox News host Tucker Carlson also joined Trump aboard Air Force One ahead of an interview with the president.

Behind-the-scenes look on Air Force One prepping for our big interview w/ Pres @realDonaldTrump. Tune in TONIGHT, 9p ET on @FoxNews! #Tucker pic.twitter.com/6KeTT8QsuO — Tucker Carlson (@TuckerCarlson) March 15, 2017

Updated at 11:15 a.m.