What is the test for striking out a collective agreement provision?

Mr. Justice Shaw in BCTF v. BCPSEA (2004) described the arbitrator’s proper mandate as follows: 36 To carry out this mandate, the arbitrator may strike out whole provisions or parts thereof where they solely relate to forbidden matters. However, where provisions relate to matters that are void as well as matters that are valid, and mere excision of words will not suffice, the arbitrator must fulfill the mandate by modifying or recasting the collective agreement provisions. The arbitrator may adopt any reasonable modification that achieves the end of getting rid of the void aspects of a provision while preserving the valid aspects. 37 By way of illustration, I pose a hypothetical example. A provision says "All teachers will wear uniforms". A law then requires that secondary school teachers be deleted from this provision. It is clear that simple excision of words will not work; but recasting of the provision will. The provision may be modified to read: "All teachers, except secondary school teachers, will wear uniforms". Another solution would be to add a sentence which reads "However, secondary school teachers will be exempted from this provision".