Dear Mr. Samba,
This is a legal requirement, if any contractor engaged contractual menpower at any site. At the time of closure of contract, he is supposed to give one month notice to the employees. Bcoz removing the contractual employees all of a sudden (on ending of the contract) will be wrong decision from legal and ethical point of view.
You have not specified that you are from PE (Principal Employer) or a contractual menpower also specify the nature of contract.
If the contract is ending from contractor's point of view only, but the contract work will be continue with some other contractor.
In that case the contractual menpower can be enrolled by the new contractor (depend upon the nature of work, nature of the contract etc).
But keeping himself safe the contractor has taken right decision on his part.