Sadiq Khan confirmed 21 transport workers have died after testing positive for coronavirus. They include 15 bus workers.
London's Mayor said he was doing everything he could "to keep transport workers and passengers safe".
Unions have called on Transport for London to provide masks and gloves for Tube and bus drivers.
Mr Khan said TfL was trying to find supplies of personal protective equipment.
I know staff are worried and many have asked for PPE, so we are working closely with the trade unions to address concerns. There are clearly issues in the supply of PPE, with hospitals and care homes reporting shortages, but I’ve also asked TfL to look into the availability of PPE stock for transport workers, in case advice from public health experts changes.