Is professional tax (PT) mandatory?

Yes, professional Tax or PT is mandatory. 

Consequences

1. Fails to Get Registration: He/she is liable to a penalty for the period during which he/she remains unregistered.
2. Fails to Deposit to the Government/ Late Deposition: He/she is liable to a penalty for the period during which he/she remains unregistered.
3. Non-Deposition of Amount: The officials have power to recover such amount along with applicable penalty and interest from the assets of such defaulter. Moreover, they can attach his/her bank account also. In serious cases, prosecution case also can be filed.