Police Minister Judith Collins says an incident in Rotorua, in which boy racers pelted patrol cars with bottles and verbally abused police officers, proves why tougher laws to fight boy racers are needed.
Thirty one arrests were made when 900 people and 230 cars gathered in the city on Friday night.
The event was supposed to be a peaceful demonstration against planned legislation to allow cars used in illegal street racing, to be seized and confiscated.
But Ms Collins says if boy racers operate within the law, the Vehicle Confiscation and Seizure Bill won't affect them.
She says they are using the bill as an excuse to be violent. She describes them as hoons and thugs.
Out of town racers involved - police
Meanwhile police in Rotorua say the incident was a "one-off".
Senior Sergeant Denton Grimes says some of the boy racers came from Auckland, Napier, Tauranga and Taupo.