Senior Tory MP Steve Brine is being investigated by the Parliamentary Standards Commissioner over claims of lobbying the NHS during the Covid crisis.
The probe into Mr Brine - the Chairman of the Commons Health Committee - was opened on Wednesday by Parliamentary Commissioner for Standards, Daniel Greenberg.
The body said the matters under investigation included "paid advocacy" and a "declaration of an interest".
WhatsApp messages leaked earlier this month claimed the ex-minister pressed the then NHS Chief Executive Sir Simon Stevens to hire anaesthetists through Remedium - a company he had worked for.
According to the MPs' register of interests, he received £1,600-a-month from the firm for his work as a "strategic adviser" between July 2020 and December 2021.
According to the Daily Telegraph, Mr Brine contacted Michael Gove - the then Cabinet Office minister - in early 2021, in the midst of the pandemic, seeking his help after he had tried to raise the issue with Sir Simon.
In a message to Mr Gove he wrote: "Dear Michael ... sorry to raise this but having tried the Dept of Health (seemed logical) and the Chief Exec of NHSE (ditto) I am at a loss.
"Long story short, I have been trying for months to help the NHS through a company I am connected with - called Remedium.
"They have 50 anaesthetists right now who can be in the country and on the ground in the NHS if someone only said let us help. They just want to assist and asked me how they might.
"Despite offering this to health and to Simon Stevens I've had nothing despite SS telling the press conference last week this is an acute problem, despite the PM telling the Liaison Committee this is his biggest problem etc etc.
"How might I progress this or does the NHS just not need the help?"
Mr Gove was said to have forwarded the message to the Health Secretary Matt Hancock in February 2021 and during the country's third national lockdown.
Mr Hancock replied: "Weird - he hasn't texted me". He added a short time later: "This is already in hand. Thanks for pinging on".
Under Parliament's rules, MPs are not allowed to lobby for any organisation they are being paid by for six months after their last remuneration.
Liberal Democrat Health spokesperson Daisy Cooper MP called on Mr Brine to step aside from the Commons Health Committee while the probe takes place.
She said: "It is absurd for an MP who may have wrongly lobbied the NHS to now be in charge of holding them to account."
"To the public, this whole thing stinks of another Conservative sleaze scandal."
Mr Brine told The Telegraph earlier this month: "This was about responding in the national interest to an urgent public call from ministers and the NHS in a national crisis even, if, ultimately, it led nowhere let alone secure any business for Remedium".
The Mirror has contacted Mr Brine for comment.
