Clarification requested for Professional Tax

Dear Sirs,

I run a proprietorship firm (unregistered) at Chennai & we offer software development / web designing services purely for overseas market. All developers / designers in our firm receive a minimum annual salary of 2.0 lakhs plus.

Are we covered under Professional Tax? I am not able to find the corresponding law or rules regarding the same, hence this request to guidance?

Pls. advise on what should be done? and how we should go about this?

Thanks & Regards,

Rajesh