Lincoln MP Karl McCartney has come under fire for accepting tickets to the Chelsea Flower Show from the world's third largest tobacco company.
The Tory MP accepted hospitality totalling more than £1,300 from Japan Tobacco International (JTI), which produces Benson and Hedges and Silk Cut, in May.
The details were declared by Mr McCartney in the Register of Members' Interests.
Now, health charities have described his acceptance of the tobacco giant's hospitality as "disappointing" and the chairman of the All-Party Parliamentary Group (APPG) on Smoking and Health, Stephen Williams, has renewed calls on the Government to tighten up the regulation of lobbying.
Mr Williams, who is the Liberal Democrat MP for Bristol West, made the demand after it was revealed that Mr McCartney wrote to the APPG on Smoking and Health asking for details of how the public health charity Action on Smoking and Health (ASH) is funded.
The letter also requested details about the number of people associated with ASH who have placements with the Department of Health and other areas of Government.
Mr Williams said: "I would expect every Member of Parliament to consider carefully what message they send out about the importance of public health if they accept hospitality from tobacco companies."
Martin Dockrell, director of policy and research at Action on Smoking and Health, said: "The Prime Minister says corporate lobbying goes to the heart of why people are fed up with politics and he is right.
"The Government's tobacco plan warns of the dangers of tobacco industry attempts to influence health policy.
"MPs don't always know when they are being lobbied by the big tobacco companies because they often hide behind a smokescreen of lobby firms and front groups."
Eileen Streets, director of tobacco control at the Roy Castle Lung Cancer Foundation, said "We are very disappointed to hear that Mr McCartney has accepted a hospitality package offered by a tobacco company."
Before winning the general election, Mr Cameron said in February 2010 that lobbying was an issue that "has tainted our politics for too long".
Existing rules on lobbying say MPs must not place themselves under any financial obligation to outside individuals or organisations and must not act as a paid advocate in any parliamentary proceedings.
Mr McCartney was unavailable for comment.