Rightly said by Umakanthan sir. The post related to taking strategic decisions, close supervision, and monitoring should be done by direct employment, while jobs related to day-to-day activities, assistance, and supporting staff can be done through Contract Labour.
Even when we apply for a Labour Licence/Registration Copy (RC), the Labor Officer demands an affidavit certifying that "workmen employed by me/my company (contractor) are not performing the same and similar kind of work as the workmen directly employed by the establishment (PE) are performing."
Moreover, when you engage Contract Labour, clearly mention in the Agreement: "It is clearly understood and agreed by and between the parties that PE shall not be held responsible or liable under the laws that are in force and that may come into force from time to time, in respect of the personnel of the Contractor, and the Contractor alone shall be solely responsible for their terms and conditions of services, safety, etc., and on no account shall the personnel of the Contractor be deemed to be employees of PE."
Hope this clarifies the matter in detail.