We recently awarded a best value contract for a construction project to a small business concern who proposed to use a subcontractor to perform the actual construction work. The prime submitted technical capabilities, resumes, and past performance of their sub to meet the technical requirements of the solicitation and would not have even been considered without the information provided on the sub. Technical was the most important factor and the technical strengths of the prime's proposal (thanks to the Sub) was the prime reason the they won the contract. Fast forward a few weeks to a couple of days before the work is scheduled to begin and we find out that the prime is going to use a different sub. I should mention that the prime never informed us of their decision to use a different sub and that we found out only by doing a little digging. I have two issues with this and wanted to see if I'm off base at all in my thinking that this warrants a T4D. 1) Endangering the performance of the contract: Since we didn't evaluate the technical capabilities and experience of the new subcontractor, we don’t know if they will be able to meet the technical requirements of the contract. We could evaluate them now before we issue the Notice to Proceed, but this wouldn't address what I think is the more serious issue regarding the source selection process. 2) The award is now protestable: The award decision was based largely on the proposed subcontractor’s technical capabilities. If the unsuccessful found out that awardee’s subcontractor changed after award, I think they would have grounds to protest (and win). If they lost to the combined proposal of the awardee and proposed sub, and now that particular sub isn't even in the picture, doesn't that invalidate the source selection decision? Also, the prime is not following through with what they promised to offer (sub’s technical expertise). I’m sure it can be argued, as the prime is doing, that nothing has changed because the new sub is just as good or better (technically) than the proposed sub; however, if the Government allowed contractors to do this, what would prevent a prime from proposing to use the World’s Best Sub for every solicitation to get the award and then change to a different sub once award has been made? Even if you can’t prove the contractor misrepresented their intentions, it still doesn't seem right or fair. Thoughts?