So, this is really a “scope” question and whether or not new task/delivery orders against the contract are within scope.  We have answered many, many questions related to scope here at AAP over the years.  A search here may come up with something similar to your situation.  But here’s a short response to your scenario.

Because of the background information you provided, we’ll assume this is not a multiple award contract requiring you to follow the procedures at FAR 16.505 or a requirements or definite quantity contract.  And that you have not exceeded the maximum order threshold in your contract.  As a result, FAR part 6 may not be applicable if the conditions at FAR 6.001(e) applied to your original procurement.  If those conditions did not apply to your original procurement then you would have to follow FAR part 6 and possibly re-compete.

That said, the fact you entered into a CPFF contract in the first place means there was a lot of uncertainty in future requirements  Therefore it was probably determined that the type and quantity of work could change or at least fluctuate.  So it is possible the original contract anticipated your scenario.  You should look in the contract file and read the justification for selecting a cost reimbursement type contract [see FAR 16.102(d) and 16.301-2(b)].

If the labor categories or materials associated with your basic contract have changed and it needs to be modified in order to add new labor categories or materials, then FAR part 43 would apply.  If doing this unilaterally, then the changes clause in your contract would apply and you are restricted by the limitations in your changes clause (most likely 52.243-2).  If you are doing this bilaterally then the generic scope test applies:

You must ask yourself; is the change within the general scope of your contract?  To answer this is a two-pronged test used by courts and boards, to comply with CICA.  It goes like this:

1) Is it reasonable to assume that a change of this nature would have been contemplated at the time of award?  If “no”, it would not be within the general scope of the contract and either you would need to re-compete or do a J&A for other than full and open competition to modify the basic contract.

If “yes” it was reasonably contemplated, then you must ask yourself “if it was known we would have made this change; would it have altered the field of original competition?”  Would different companies have provided an offer, would companies that did propose chosen not to propose, would offerors have altered their cost/pricing strategy, etc.?

If the answer to that is “yes”, then again it would be out of general scope (cardinal change) and you would need to re-compete or do a J&A for other than full and open competition to modify the basic contract.  If the answer was “no”, then it is within general scope and you could modify the contract to add/delete labor categories or materials.

These are highly scenario dependent and subjective in nature.  But again the fact you have a CPFF contract makes it easier (baring any other information in your contract file limiting the purpose of the contract) to conclude you are within the general scope of your contract.

About the only consequences you face (outside of scrutiny from your contracting chain of command) would be that an unsuccessful offer of your original competition could complain the new orders you are executing are out-of-scope, cardinal changes.

We highly recommend you discuss your scenario with your contracting leadership and contract legal counsel.