Transport for London have handed out 1,700 fines to people who refuse to wear masks when travelling.
There are now 500 TfL enforcement officers working to ensure public transport users comply with the rules.
Wearing a mask on the tube, trains and buses has been mandatory since June last year but still a minority ignore what is being asked of them.
Some users are, however, exempt from wearing face coverings on medical grounds.
People not wearing a mask can be fined anything from £200 to £6,400, for repeat offenders.
In addition to fines, TfL say 9,300 passengers have not been permitted to board and 2,100 have been ejected.
Enforcement officers are looking to target specific areas of London where TfL staff have reported the greatest disregard for the rules.