Boris Johnson has been accused of trying to change parliament’s rules to allow “cash for access”.
Owen Paterson, a former Conservative cabinet minister, faces a 30-day suspension from the Commons.
He was found to broken the rules by using his position as an MP to lobby on behalf of companies he worked for.
But he could escape punishment as Downing Street is backing a change of the disciplinary process which will be voted on later on Wednesday.
Speaking during PMQs, Labour’s deputy leader Angela Rayner accused Johnson of “cheating the public”.
“It is one rule for everybody else and one rule for the Conservatives. When they break the rules, they just remake the rules,” she said.
“In no other profession in our country could someone be found guilty by an independent process and just have their mates vote them back into the job.”
Referring to a misconduct case against Delyn MP Rob Roberts, Rayner added: “When a Conservative member was found guilty of sexual harassment but let off on a loophole, they said the rules could not be changed after the event.
“So they can’t change the rules to stop sexual harassment but they can change the rules to allow cash for access.”
The prime minister defended the planned change and said it was necessary to allow Paterson a “proper appeal”.
“All the professions that she mentions have a right of appeal. That is what the House needs to consider,” he said.
Rayner was standing in for Keir Starmer, who is still isolating at home having tested positive for Covid.
The Commons will vote on whether to approve the six-week ban from parliament for Paterson after an investigation by the Parliamentary Commissioner for Standards found he repeatedly lobbied ministers and officials for two companies paying him more than £100,000 per year.