Jack Straw, Labour foreign secretary when Britain helped invade Iraq in 2003, and Malcolm Rifkind, a senior figure in Prime Minister David Cameron's Conservative party, were accused in a probe by the Daily Telegraph newspaper and Channel 4 television.
Both deny any wrongdoing but are the latest in a wave of lawmakers to be accused of seeking to profit from offering private companies privileged access to advance their interests.
In a sting by undercover reporters, the two politicians are said to have offered to act on behalf of a fictitious Hong Kong-based company at a price of at least USD 7,700 a day.
Rifkind reportedly said he could arrange "useful access" to every British ambassador globally.
Straw is said to have used his parliamentary office for meetings about consultancy work and claimed that he had operated "under the radar" to help change EU rules in work for a commodities firm.
Five years ago, Cameron warned that corporate lobbying was the "next big scandal" waiting to hit parliament.
Straw has suspended himself from the Labour party in parliament, while Rifkind has had the Conservative whip suspended, meaning both will sit in the House of Commons as independent lawmakers for now.
They now face investigations by the Parliamentary Commissioner for Standards, which investigates allegations of rule breaking by MPs.
Straw and Rifkind took to the airwaves Monday to defend themselves.
Straw insisted he had been discussing work he might do after stepping down as an MP after the May 7 general election following 36 years in office.
"There are very, very strict rules here about what members of parliament can and can't do," he told BBC radio.
"I absolutely kept not only to their letter but also to their spirit."
Rifkind, who chairs the parliamentary committee which oversees Britain's intelligence services, vowed to fight the allegations "with all my strength".
