This rule defines a subcontractor as a third party executing a portion of a primary contract. It outlines the conditions for approving subcontractor costs, which include ensuring the work relates to the main contract, costs do not exceed revenues, and proper documentation is available. The rule mandates official written approval for any assignment of the contract. The Tax Department will disallow payments if the Incorporated Body fails to provide notification or does not withhold a 5% income tax retention from the subcontractor's contract value.