Doctors must not agree to "gagging clauses" that stop them raising concerns about poor quality care, according to new guidance.
The General Medical Council (GMC) said clauses in contracts and agreements to silence doctors went against their "professional duty" to raise worries about substandard care.
The GMC has heard anecdotes from doctors about contracts which say they must not contact the regulator if they have concerns. However, the GMC says the interests of the patient must "trump everything" and doctors must not sign such contracts, which risk their own careers and the health of patients.
Niall Dickson, chief executive of the GMC, said doctors who raised concerns could feel isolated but support mechanisms were in place, including through the GMC's new liaison service.
He added: "These clauses are totally unacceptable. Doctors who sign such contracts are breaking their professional obligations and are putting patients, and their careers, at risk.
"Our new guidance also makes clear that doctors must not sign contracts that attempt to prevent them from raising concerns with professional regulators such as the GMC and systems regulators, such as the Care Quality Commission (CQC).
"Nor must doctors in management roles promote such contracts or encourage other doctors to sign them."
The guidance does say that doctors should try first to raise their concerns in their workplace, but can then go to the GMC or another regulator.
The doctor may wish to tell the GMC if they are unable to raise the issue with their employer, because they believe the employer is part of the problem or if a doctor has raised "concern through local channels but are not satisfied that the responsible person or body has taken adequate action".
Doctors should also tell regulators if there is an immediate serious risk to patients and a regulator or other external body has responsibility to act or intervene. They can then go public if they believe they have done all they can to raise concerns and if they have good reason to believe patients are still at risk of harm.