The House of Commons disciplinary procedures lack "teeth" and require urgent reform, Theresa May has warned.
In a letter to Speaker John Bercow, the Prime Minister said a situation where MPs did not have to follow procedures laid down by the Independent Parliamentary Standards Authority (IPSA) could not be tolerated any longer.
She asked for Mr Bercow's assistance in working on a cross-party basis to establish a new "House-wide mediation service" backed by a "contractually binding grievance procedure" available for all MPs.
In her letter Mrs May said she was sure the Speaker would share her concerns at recent media reports of alleged misconduct by some MPs towards staff.
"I believe it is important that those who work in the House of Commons are treated properly and fairly - as would be expected in any modern workplace," she wrote.
"As you know, there is a suggested disciplinary procedure provided by IPSA as part of the standard contract. However, it does not have the required teeth as contractually an MP does not have to follow the procedure.
"I do not believe that this situation can be tolerated any longer. It is simply not fair on staff, many of whom are young and in their first job post-education."
Mrs May said the Conservative Party had offered MPs a code of conduct on a voluntary basis but that it had no legal standing and was "not fit for its intended purpose".
"The Conservative Party is determined to protect those staff who work for MPs but in order to do so effectively I believe that we must establish a House-wide mediation service complemented by a contractually binding grievance procedure available for all MPs irrespective of their party banner," she said.
"It is vital that the staff and the public have confidence in Parliament and resolving this employment irregularity on a cross-party basis can play an important role in this.
"I would be grateful if you would be able to use your office to assist me in doing all we can to ensure that the reputation of Parliament is not damaged further by allegations of impropriety."