Maintenance Agreement Cancellation/Termination

FAR 13.302-4, Termination or cancellation of purchase orders, begins by discussing purchase orders that have been accepted in writing in paragraph (a).  In paragraph (b), it then discusses purchase orders that have not been accepted in writing.  In that context, it ends, "If the contractor does not accept the cancellation or claims that costs were incurred as a result of beginning performance under the purchase order, the contracting officer shall process the action as a termination prescribed in paragraph (a) of this section."

This leads me to believe that if the purchase order was accepted in writing or if you know the contractor has partially performed, then cancellation isn't an option.

I don't see the word cancellation outside the context of solicitations in my day-to-day work, so my apologies if I'm misunderstanding your question.

Edit:

I see FAR 49.402-3(a) uses the phrase, "no-cost cancellation," but I think it just means a bilateral no-cost termination

I also see FAR 42.302(a)(63), which lists as among the contract administration functions normally delegated, "Cancel unilateral purchase orders when notified of nonacceptance by the contractor.  The CAO shall notify the contracting officer when the purchase order is canceled."  So you may want to be mindful of that unless you are both the PCO and ACO.