An executive agency shall require that a covered contract provide that if the contractor submits to the executive agency a proposal for settlement of indirect costs incurred by the contractor for any period after such costs have been accrued and if that proposal includes the submission of a cost which is unallowable because the cost violates a cost principle in the Federal Acquisition Regulation (referred to in section
421
(c)(1) of this title) or an executive agency supplement to the Federal Acquisition Regulation, the cost shall be disallowed.