The question of applicability of service tax under RCM depends upon the nature of service provided and legal status of entity. As per Item No. 8 of the Notification No. 30/2012 dated 20.06.2012, the service tax in respect of manpower supply (temporarily or otherwise to another person to work under his superintendence or control) provided by individual, HUF, proprietary firm or partnership firm including AOP provided to a business entity registered as a body corporate is partially payable by service provider and partially payable by service receiver. However, if service is provided by body corporate then only service provider is liable to pay service tax.
Assumption ; Since from query, the nature of service provider and service recepient is not clear, it is assumed that agency is not a body corporate and service recepient is a registered as a company.
Conclusion: If the Agency's responsibility is supply labour/man power and the execution of work is the responsibility of Agency, then it does not come under Reverse Charge Mechanism. If the contractor responsibility is supply labour/man power and the execution of work is the responsibility of your company, then it is manpower contract. and accordingly, the service tax to the extent of 75% is payable by recipient of service and balance by service provider.
Note: If the contract is for doing/execution of works under the supervision of contractor and penalty is levied for delay etc then it is not covered under Manpower contract. Contract agreements need to be studied accordingly.
Thanks.