Just got a response from CP trip trades:

Section 25, pg. 38; G.3

g. Denial of Swap(s) or Drop(s)
The Company will not deny a Schedule Adjustment Request unless it violates the Agreement, the FARs, or the provisions listed below:

(3) A swap or drop request will be granted unless its approval would result in an inadequate level of Reserve coverage on any day that the dropped Trip operates.