A unit may assert a contract claim against a contractor by sending written notice to the contractor and the procurement officer that states: the basis for the contract claim; to the extent known, the amount, or the performance or other action, requested by the unit in the contract claim; and the date by which the contractor is required to provide a written response to the contract claim. On receipt of a contract claim from a unit, a procurement officer: shall review the substance of the contract claim; may request additional information or substantiation through an appropriate procedure; and may discuss or, if appropriate, negotiate the contract claim with the unit or contractor. The procurement officer shall proceed under subsection (b) of this section if the contractor fails to respond, provides an inadequate response, or denies the contract claim or the relief sought by the unit in whole or in part. If the contractor and the unit do not resolve the contract claim, the procurement officer shall prepare a proposed decision on the contract claim, including: a description of the contract claim; references to pertinent contract provisions; a statement of factual areas of agreement or disagreement; and a statement in the proposed decision wholly or partly granting or denying the relief sought, with supporting rationale. Unless otherwise provided by regulation, the procurement officer shall submit the contract claim and proposed decision to: the head of the unit; and the head of the principal department or other equivalent unit of which the unit is a part. The reviewing authority shall approve, modify, or disapprove the proposed decision. In disapproving a proposed decision, the reviewing authority may remand the contract claim with instructions to the procurement officer. On remand, the procurement officer shall proceed as required under this subsection and in accordance with the instructions of the reviewing authority. The decision of the reviewing authority is the final action of the unit.