The overarching guidance on whether or not the contractor has the right to submit a post-award proposal are based on the nature of the contract change and the contract clause embedded on your contract that deals with contract changes. Since your scenario deals with an active cost-type contract, I am assuming you have FAR Clause 52.243-22 Alternate I Changes - Cost-reimbursement in your contract. In a nutshell, the Contracting Officer has the unilateral right to make changes within the scope of the contract if the changes deals with description of services to be performed, time, or place of performance. In turn, the clause gives the contractor the right to request an equitable adjustment in a form of a cost change proposal. Any contract changes not listed on this above clause requires both mutual agreement of both parties, i.e. buyer and seller have to negotiate and agree on the contract change prior to execution. This also requires the contractor submitting a cost change proposal for the government to evaluate and reach a negotiated settlement with the contractor. In your case, a reduction of the performance work statement for services is a change of the terms and conditions of the active contract; therefore, the contractor has the right to seek an equitable adjustment in response to de-scoping the work both parties originally signed-up for. The fact that this is a cost-type contract is irrelevant when dealing with changes to the terms and conditions of the active contract.