Service tax input credit in construction

Dear All!

My client is engaged in construction Industry and they are taxable for different projects. They adjust input credit of service tax only with the service tax liability of that respective project, and do not take credit for a different Project. Due to this, there is huge amount of input credit for a particular project for which there is not much of service tax liability. 

My Query is does the service tax rules state that inout credit should be adjusted on Project specific basis?

Please clarify with appropriate notifications.

Thanks in advance!