Most of the answers are not appropriate when we are talking about contract workers. Please be specific about the kind of work you are demanding from them and who the decision-maker or primary employer will be. If your company will be held as an employer due to having all the administrative and management control over the workers, your company will be liable for all legalities and payments, and the role of the agent or contractor plays no role. Please refer to the Hussain Bhai Calicut case citation.
If you enter into a renewable contract, the same will be invalid. Refer to the Uma Devi case citation. If you hire workers for a period of less than 240 days, give them a rest, and then rehire them or anyone else, you will be liable for unfair labor practices. Review the Tata Motors case from the Mumbai High Court.
In simple terms, only involve an agent or contractor if you have a job that cannot be performed by you or if you do not have the required specialization. Hire directly onto your payroll.