@ Shanti019
If there bills are shown as Service Exp, pls note the below points:-
1. If the bill value (monthly/annual) comes under TDS Act, than TDS must be deducted (as per applicable sections/s). Ask them to submit their PAN, otherwise higher TDS is applicable.
2. It is advisable to issue an service agreement (duly mentioning all commercial, statutory & legal terms.
If you want to cover them under PF-ESI than note the below points:-
1. Their wages needs to be booked under single factory (Same PF-ESI Codes).
2. The Wages must be as per MW Act.
3. It is observed such labours never interested to reduce their Net Amt/Take Home Salary, so you have to increase their wages.
4. After covering them as an employee, it will attract other liabilities as well (Bonus, Gratuity, Leaves etc).
As per my opinion make a thorough observation if you can give full time work (if they can be engaged in other tasks as well) than only go for PF-ESI, otherwise continue them as Contract for Service. But strictly follow above mentioned basic points.