The doctrines of paramountcy and interjurisdictional immunity are fundamental for harmonizing the exercise of powers by different orders of government in a federal state. Paramountcy provides clarity where there is overlapping jurisdictional control over a submject matter of legislation. Interjurisdictional immunity provides clarity where provincial regulations significantly interfere with a federal prson, thing or undertaking.

The paramountcy doctrine becomes relevant where both the federal and provincial legislation are intra vires. The two enactments "meet" in the sense that they simultaneously govern the activities of a citizen. Paramountcy is necessary where the citizen cannot simulataneously obey each legislative command because the commands give contradictory signals. The federal legislation instructs the citizen to go left; the provincial legislation instructs the citizen to go right. Paramountcy is also relevant where a provincial command would weaken the enforcement or confuse the citizen about the purpose of the federal legislative command. When there is a conflict such as this, the federal legislation prevails. Paramountcy is meant to maintain the ability of federal regulatory regimes to have their full range of legislative effects including necessary and subsidiary implementing features.

The interjurisdictional immunity doctrine is far more troubling for academic commentators and courts alike. Often, the courts consider interjurisdictional immunity to be a subset of paramountcy; still others believe the terms are synonymous. They are not. Interjurisdictional immunity does not consider two pieces of legislation, one federal and one provincial, which meet. In fact, there need not even be any conflicting federal legislation (although often there is). Interjurisdictional immunity instead becomes relevant in the situation where there is a federal person (such as an Indian, or a postal carrier), thing or undertaking (such as an airport or a harbour) which exists. The provincial legislation significantly regulates the federal person, thing or undertaking in such sense as to bring its federally-recognized personality into question. In short, interjurisdictional immunity becomes relevant where provincial regulatory regimes would change these crucial elements that bring the thing or person within federal jurisdiction or destroys the juridical life or status that federal jurisdiction allows.

It should be noted that there is no such thing as a "federal enclave" in which all federal persons, things, and undertakings are immune from provincial legislation. Indians do not receive exemption from provincial speed limits, even on reserves. But, where the operation of the provincial legislation affects the federal thing, person or undertaking in such a way that it is ‘significantly harmed', or the status allowed by federal jurisdiction is significantly changed, the provincial legislation will be considered to be inoperative.

In Constitutional Law of Canada, 8th edition, at pp. 282-283, I provide analysis of "how immune" a federal undertaking is from provincial legislation. In this section, I note the confusion caused by Irwin Toy, in particular, how it appeared to Professor Hogg (and others) that the Court had returned to an "impairment" test instead of a "affect a vital part" test. As a postscript to this commentary, it should be noted that in National Battlefields (p. 285), Justice Gonthier held that the provincial legislation was inoperative. It might be concluded from this example that the true "impairment" test includes a provincial legislation which gives the province capacity to impair.

There is one additional consideration in the interjurisdictional immunity debate. There is some question as to whether a provincial statute should be "read down", held to be "inapplicable", or held to be "inoperative". I believe the correct term to be used is "inoperative". Reading down is a concept which is best reserved to legislation which is, but for the reading down, ultra vires. As stated above, interjurisdictional immunity assumes, at a minimum, that vires is not an issue.

For more information on paramountcy and interjurisdictional immunity, consider the following cases:

Husky Oil Operations v. MNR
Bank of Montreal v. Hall
Clarke v. Clarke
Ontario Hydro v. Ontario (LRB)

Interjurisdictional Immunity

Ordon Estate v. Grail
Canada (National Battlefields Comm.) v. Commission de Transport
Irwin Toy Ltd. v. Quebec
Ontario Hydro v. Ontario (LRB)
Delgamuukw v. B.C., at para 177-183 especially.