Please go through the provisions of The Contract Labour (Regulation & Abolition) Act, 1970, which are as follows:
Section 1 - Short Title, Extent, Commencement, and Application
Sub-section 4) It applies -
a) To every establishment in which twenty or more workmen are employed or were employed on any day of the preceding twelve months as contract labour.
b) To every contractor who employed or who employed on any day of the preceding twelve months twenty or more workmen.
Section 7 - Registration of Certain Establishments
(1) Every principal employer of an establishment to which this Act applies shall, within such period as the appropriate government may, by notification in the Official Gazette, fix in this behalf with respect to establishment generally or with respect to any class of them, make an application to the registering officer in the prescribed manner for registration of the establishment:
PROVIDED that the registering officer may entertain any such application for registration after the expiry of the period fixed in this behalf, if the registering officer is satisfied that the applicant was prevented by sufficient cause from making the application in time.
(2) If the application for registration is complete in all respects, the registering officer shall register the establishment and issue to the principal employer of the establishment a certificate of registration containing such particulars as may be prescribed.
I think the above information is sufficient regarding your query.
Thank you.