Three peers have been accused of agreeing to carry out Parliamentary work for payment, the BBC reported.
Undercover Sunday Times reporters filmed the men appearing to offer to help a fake solar energy company.
Ulster Unionist Lord Laird and Labour’s Lord Mackenzie of Framwellgate and Lord Cunningham deny wrongdoing.
The two Labour peers have been suspended from the party and Lord Laird has resigned the party whip pending an investigation.
In a separate investigation by the BBC’s Panorama programme in conjunction with the Daily Telegraph, Lord Laird was also secretly filmed discussing a retainer to ask parliamentary questions.
The House of Lords code of conduct says peers must not act as paid advocates and “must not seek to profit from membership of the House by accepting or agreeing to accept payment for providing parliamentary advice or services”.
Lord Laird is alleged to have told reporters posing as lobbyists for a fake company representing business interests in Fiji that he would be interested in accepting a retainer of £2,000 a month.
He told the Panorama undercover team that he would help start an All Party Parliamentary Group for Fiji. He indicated that he would use the promise of a trip to Fiji as a “bribe” in order to get people to join the group.
The MPs deny any agreement to operate in breach of the House of Lords code of conduct.
Panorama will be shown on BBC One at 21:00 BST on Thursday.