Police said the advocates boycotted the district court as part of their agitation against the helmet rule which came into force on July 1, held a demonstration and raised slogans in front of the court complex.
The Madras High Court, in an order on June 8, made it clear that wearing of helmets by two-wheeler riders is a must and documents including driving license must be impounded in case of failure to do so.
Police re-inforcement had been put in place in the court complex to monitor the situation.
The advocates have been taking out out vehicle rally blatantly violating the orders of Madras High Court and Tamil Nadu government.
While 99 per cent of the riders obeyed the order by wearing helmet, the advocates of the district court were openly defying the rule, a city traffic police official said.
Cases against 100 advocates have been registered for not wearing helmets, police said.