Annual return submission to labour inspector in Tamilnadu is mandatory or optional?

Dear all, Annual return submission to labour inspector in Tamilnadu is mandatory or optional?

Dear Sirs,
Our Establishment had obtained Two Labour Licences, but LIN not seeded. The question is the time period for fill annual returns are very near. And after filling of common annual return submitted the same to CLC(Central) but not received acknowledgement. Is there any problem? Please clarify the same..
Guru Swamy, Manager.