part. Interjurisdictional immunity under COPA and PHS Community Services In Quebec (AG) v Canadian Owners and Pilots Assn ("COPA"), Chief Justice McLachlin outlined a two-step test that must be undertaken to determine if interjurisdictional immunity comes into play: Does the provincial law trench on the protected "core" of a federal competence? Is the provincial law's effect on the exercise of the protected federal power sufficiently serious to invoke the doctrine of interjurisdictional immunity? Though there remains some debate, it has generally been accepted that interjurisdictional immunity applies equally to both the federal and provincial governments. Nevertheless, virtually all of the case law concerns situations where provincial laws encroach on federal matters. In Canada (AG) v PHS Community Services Society, the Supreme Court expressed caution in employing the doctrine in future cases because: It is in tension with the dominant approach that permits concurrent federal and provincial legislation with respect to a matter. It is in tension with the emergent practice of cooperative federalism. It may overshoot the federal or provincial power in which it is grounded and create legislative "no go" zones where neither level of government regulates. As Chief Justice McLachlin explained in that decision: Footnotes and citations References Case citations Constitution of Canada