About three of the UK capital's parking attendants are assaulted every day, according to the Association of London Government (ALG).
Attacks on attendants have included being run over, shot at and attacked by groups with baseball bats.
The ALG report also says fines are not handed out purely to make money and any profit has to, by law, go back into transport and the environment.
The evidence is being presented to the London Assembly on 10 February.
Phil Portwood, from the ALG, said: "This is very serious, and while being a parking attendant is never going to be the most sexy job in the world they have the right to expect not to get attacked or assaulted in the line of their duties."
The report showed of the 29 boroughs listed in the report two made losses from their parking schemes and 24 made less than £4m.