More than 160 cyclists were found to be flouting road safety laws during a six-hour police crackdown.
Hampshire Police are getting tougher on unsafe cyclists
Officers in Portsmouth stopped cyclists riding without lights or on the pavement at five different city checkpoints.
Usual £30 fines were dropped during the operation and warnings given instead.
But Hampshire Constabulary and council road safety officers said police would be getting tougher from now on.
Peter Bruce, road safety officer for Portsmouth City Council, said: "It is amazing the number of people who ride around without lights.
"From Monday there will be a much tougher stance taken on this and on cyclists who ride on pavements.
"The only time this is acceptable is when there is a legitimate cycle lane on a pavement."