Pith and substance, interjurisdictional immunity or paramountcy? The NCA Constitutional Law framework

These three doctrines answer three different questions: is the law valid, does it apply to this matter, and does it still operate alongside a federal law.

Mixing them up is a frequent mistake in division-of-powers answers. Here is how they fit, using the cases on the Constitutional Law syllabus.

1. Is the law valid? Pith and substance

Characterize the law by its purpose and effects, then classify it under the heads of power in ss 91 to 95 (R v Morgentaler, 1993). A provision that intrudes on the other level's power may still be saved as ancillary to a valid scheme (General Motors v City National Leasing, 1989). Under the double aspect doctrine, both levels can legislate on the same subject from different angles.

2. Does a valid provincial law apply to a federal matter? Interjurisdictional immunity (IJI)

The question is whether the provincial law impairs the core of a federal head of power, not merely affects it. Canadian Western Bank (2007) says to use the doctrine with restraint, mostly where earlier cases have already recognized the core. Quebec (AG) v COPA (2010) is the example where it applied: a provincial agricultural zoning law that impaired the core of federal power over aeronautics.

3. Two valid laws: does the provincial one still operate? Paramountcy

Is there an operational conflict (you can't comply with both), or does the provincial law frustrate the federal purpose? If so, the provincial law is inoperative to the extent of the conflict (Rothmans, Benson & Hedges v Saskatchewan, 2005).

Order in an exam answer: settle validity first. Canadian Western Bank also signalled that, without precedent favouring IJI, paramountcy will usually be the better tool.

A recent case worth knowing: Opsis (2025)

In Opsis Airport Services v Quebec (AG), 2025 SCC 17, decided unanimously on 30 May 2025, the Supreme Court held that Quebec's Private Security Act was inapplicable to companies doing security work at Montréal-Trudeau airport and a marine terminal: the work fell within the core of federal aeronautics and shipping, and provisions letting the provincial regulator suspend licences and issue directives impaired that core. Because those provisions couldn't be severed, the Act as a whole was declared inapplicable to them. The Court confirmed IJI needs both an intrusion on the core and a serious impairment of it, and held that impairment can be shown from what the legislation allows, without waiting for it to happen. Opsis postdates the January 2023 syllabus, so build your answer on the syllabus cases and treat Opsis as context.

Question for the board: reading a fact pattern cold, what tells you which of the three questions you're actually being asked?