The contractor is also an employer, and in respect of the employees hired by him, he is the employer who has to take care of the employee benefits and welfare. Therefore, allowing 26 weeks' leave on account of maternity and paying maternity bonus, etc., are to be done exclusively by the contractor. At the same time, the contract is for deploying a required number of persons on a daily basis. If X is on leave, the contractor is expected to send another person, Y, to the plant/site. For the principal employer, it does not matter who is doing the work, but what is important is whether work is being done by the employee(s) of the contractor.
The above being the legal side, in respect of some contracts, wherein the contractor is asked to deploy persons with special skills or persons identified by him, then the contractor will be sourcing persons with such special skills or persons suggested by the principal employer, as the case may be, exclusively for the principal employer. If that employee has to undergo long leave with pay, say maternity leave, then the employer will have to bear the cost of retaining the person.
In either case, if the employee is covered by ESI, the ESIC will take care of her leave and benefits. Ultimately, the contributions paid by the contractor towards ESI are a cost to the principal employer only because it will be the total cost including the wages, contributions towards PF, ESI, etc., and other benefits like bonus by way of deploying employees that will be agreed to be paid to the contractor. As such, whenever the contractor is asked to deploy a woman employee on a salary above the ESI limit, he should factor the maternity benefits payable in the cost of deployment, or should reach an agreement as to the treatment of the maternity period with the principal employer.