Transport for London (TfL) is raising its penalty fine for those who dodge bus fares from £5 to £10.
Bus fare inspections will also be increased
The move is an attempt to claw back some of the £15m to £20m of revenue it says is lost every year.
"We think it will really increase the deterrent effect," said Jerone Wymar from TfL.
"We are also increasing the number of revenue inspectors who check people. We are concentrating them in places where we think we have a bigger problem."
Only 16% of passengers pay with cash in central London, according to TfL figures, with the majority of bus users having travel passes, ticket books or the Oyster card.