NHS officials have considered telling paramedics they must be clean shaven to protect themselves from coronavirus.
London Ambulance Service said in a draft memo - seen by the BBC - that its ability to handle potential Covid-19 cases was "adversely affected" by crews unable to wear respirators properly.
The service said staff had been asked to consider shaving but it had decided against mandating they do so for now.
The Department of Health said there was no national policy on the issue.
The London Ambulance Service NHS Trust - which employs first responders across the capital - wrote in the unsent internal bulletin that "all staff in patient-facing roles must be clean shaven when on-duty".
The trust's current policy asks staff to consider shaving to ensure respirator masks fit tightly against the face.
The draft memo, issued to a group of managers on Saturday, said the service's "ability to respond to potential Covid-19 patients has been adversely affected by the low availability of crews who are successfully [tested for respiratory masks], which is partly driven by crew staff not being clean shaven".
The memo said 50 clinical staff had failed so-called "fit tests" for protective masks due to their facial hair.
The memo suggested staff with protected characteristics - such as religious beliefs or a disability - who could not clean shave would "be engaged with on a case-by-case basis and a number of alternative options have been identified to support this".
A later email to staff, seen by the BBC, said the trust had chosen to hold off issuing the new policy until further guidance from Public Health England.
The Health and Safety Executive has said poor-fitting respirators can be "a major cause of leaks".
"If there are any gaps around the edges of the mask, 'dirty' air will pass through these gaps and into your lungs," it added on its website.
Last month, an NHS trust in Southampton asked frontline staff to consider shaving facial hair to ensure respirators fit properly.
And a 2017 poster published by the US Centre for Disease Control and Prevention showing suitable styles of facial hair for use with respirators was re-circulated online.
It was announced on Saturday that the number of confirmed coronavirus cases in the UK had risen above 200, with more than 21,000 people tested so far.
The Department of Health said it was for local NHS trusts to devise policy regarding respirators and facial hair.
Public Health England said it had no plans to issue guidance on the issue.
A London Ambulance Service spokeswoman said: "The trust has asked clinical staff to consider shaving to undergo [respirator mask] fit testing and then remaining clean shaven to maintain compliance.
"We continue to adapt our response and one of the things we have considered is mandating staff to be clean shaven. However, we have not taken this step as the advice is changing quickly and we are awaiting further guidance from Public Health England in the coming days."