More than 175,000 people have signed a petition calling on the Prime Minister to sack Conservative Charnwood MP Stephen Dorrell.
Mr Dorrell has recently started working for accountancy firm KPMG and has said he will not seek re-election in May.
However the petition, on the 38 Degrees website, urges David Cameron to force Mr Dorrell to make a choice between his MP's role and his employment at KPMG as he sees out his term.
Critics of the former health secretary say there is a conflict of interest because his new job is to help KPMG get a contract to manage NHS medical records.
The petition reads: "Dear Mr Cameron, MPs should work for voters, not private companies - especially not private companies with an interest in privatising our NHS.
"Force Stephen Dorrell MP to pick a job now. It's completely inappropriate to work for KPMG, a private company that wants to bid on a £1 billion NHS contract, and stay on as an MP till May 2015.
"Please sack him from your party if he refuses to put an end to this huge conflict of interest."
Mr Dorrell told the Mercury today there was no conflict of interest between his roles and stressed he felt it was important MPs have "outside activities" beyond politics.
He said he was still committed to working for his constituents and that his 21 weekly hours at KPMG part of a working week that was "seldom less than 100 hours".
He said he would not be stepping down adding: "This is a political campaign by people trying to making a political point.
"There is no basis whatsoever that I should stand down.
"There is no conflict of interest at all. Absolutely none."
Mr Dorrell also said the David Cameron had not raised the issue with him.
Nobody from 10 Downing Street was available for comment.
The Parliamentary Standards Commissioner Kathryn Hudson had been asked to look into Mr Dorrell's position by Labour MP Graham Morris who sat on the parliamentary health select committee chaired by the Conservative.
Mr Dorrell said she concluded there was nothing improper about him holding both roles at once.
A spokesman for Ms Hudson's office said: "The commissioner has not received a formal complaint about Mr Dorrell and she is not currently undertaking any inquiry concerning him. It follows that she has not taken any view."
The Charnwood Conservative Association is in the process of picking a candidate to defend the seat in May.
It is considered a safe seat because Mr Dorrell won a 15,000 majority at the last election.
Association chairman Hanif Asmal said: "We hope to have selected a candidate in January or February.
"It has been popular. I will probably get somewhere like 200 applications."
