The doctrine of Interjurisdictional immunity is a rarely used constitutional tool that is employed to insulate the activities of one level of government from another. Thus far in Canadian case law, this doctrine has almost always been used in favour of the federal government.

Typically, interjurisdictional immunity is triggered when a province passes a law of general application, for example laws governing speed limits. These laws can often affect companies or industries, otherwise known as undertakings, which are exclusively governed by federal law. An example of this would be if a Canada Post truck received a speeding ticket. In this instance, the doctrine of interjurisdictional immunity could be invoked to attempt to stop Canada Post from having to pay the ticket because they are a federal undertaking immune from provincial law.

In practice, interjurisdictional immunity is used in only very rare circumstances. Courts have held that it is a doctrine that goes against the modern way of interpreting the Constitution, which favours co-operation and overlap . Concerns have been raised that overusing the doctrine could lead to either legal vacuums where no law would apply or to an over-centralization of power since the doctrine has traditionally favoured the federal government over the provinces.

In order to deal with these issues, the Supreme Court of Canada has created a very strict test that needs to be met in order for the doctrine to be used. The first test was adopted in the Bell Canada Case. It stated that a law had to affect a vital or essential part of an undertaking of the other jurisdiction for the doctrine of interjurisdictional immunity to be used. The Supreme Court re-evaluated this test ten years later in the Canadian Western Bank case, finding that the Bell Canada test overextended the doctrine. Under the new test, a law has to impair a vital or essential part of an undertaking in order for the doctrine to be used. The Supreme Court reaffirmed the limited scope of the doctrine and stated its preference for pith and substance analysis and thedoctrine of paramountcy.

Prominent Interjurisdictional Immunity Cases:

Bell Canada v. Quebec

Canadian Western Bank v Alberta