What is the test for determining the jurisdiction of a unionized board over a labour dispute?

This brought the judge to the leading Canadian decision on the jurisdiction of labor relations boards, Weber v. Ontario Hydro 1995 CanLII 108 (SCC), [1995] 2 S.C.R. 929. Speaking for the majority in that case, McLachlin J. (as she then was) had rejected “concurrency” and “overlapping” models of jurisdiction in favour of a broad “exclusive” jurisdiction model. The jurisdiction of labour relations boards over labour disputes was said to depend on their “essential character”. She observed: … The issue is not whether the action, defined legally, is independent of the collective agreement, but rather whether the dispute is one “arising under the collective agreement.” Where the dispute, regardless of how it may be characterized legally, arises under the collective agreement, then the jurisdiction to resolve it lies exclusively with the labour tribunal and the courts cannot try it. [At para. 43; emphasis by underlining added.] and further: … The question in each case is whether the dispute, in its essential character, arises from the interpretation, application, administration or violation of the collective agreement. [At para. 52.]