Before engaging Contractors Labour u must check whether the contractor has registration with local RPFC & ESIC office. If not then u have to cover these workers under ur PF & ESIC codes. If the contractor has the codes u must ask him to submit to you a copy of the challan evidencing payment to the authorities. As a principal employer it is your resposibility to ensure that PF & ESIC contributions are paid to the authorities. In case of any evasion authorities will held u responsible for non payment of dues.