Interjurisdictional immunity

Interjurisdictional immunity is an exception to the pith and substance doctrine, as it stipulates that there is a core to each federal subject matter that cannot be reached by provincial laws.

The doctrine renders inapplicable legislation of general application which affects the rights and obligations, impacts the status, or regulates the essential parts of: exclusively within the core of the jurisdiction of the other order of government.

This doctrine was affirmed in 1988 when the Supreme Court of Canada ruled in three cases that provincial occupational health and safety laws were held to be inapplicable to three federal undertakings engaged in interprovincial transportation and communication.

Indeed, rates and the availability and quality of services are inseparable from the wage scale that the undertaking must pay, the availability of its manpower, leave, vacation—in short, working conditions.The doctrine was modified in Irwin Toy[12] to specify that: In response to this more classical approach to settling matters of constitutional law, the necessary degree of infringement was revisited in Canadian Western Bank[13] in 2007, where the Supreme Court of Canada ruled that, in the absence of outright impairment of the "vital or essential part", interjurisdictional immunity would not apply.

This means, in practice, that it will be largely reserved for those heads of power that deal with federal things, persons or undertakings, or where in the past its application has been considered absolutely indispensable or necessary to enable Parliament or a provincial legislature to achieve the purpose for which exclusive legislative jurisdiction was conferred, as discerned from the constitutional division of powers as a whole, or what is absolutely indispensable or necessary to enable an undertaking to carry out its mandate in what makes it specifically of federal (or provincial) jurisdiction.

[22] The Supreme Court has expressed caution in employing the doctrine in future cases because:[23] As McLachlin CJ explained in Canada (AG) v PHS Community Services Society:

Its premise of fixed watertight cores is in tension with the evolution of Canadian constitutional interpretation towards the more flexible concepts of double aspect and cooperative federalism.