[4] On March 25, 2021, the Supreme Court of Canada rejected the 2019 appeal of the provinces of Alberta, Ontario, and Saskatchewan and ruled in Reference re Greenhouse Gas Pollution Pricing Act that the GHGPPA was constitutional.

[5][6][7] Commentators had varying reactions to who the ruling benefited most politically,[8][9][10] with some stating that it represented a blow to the group of conservative premiers that made opposition to carbon pricing a central aspect of their policies.

[11] The legislation aims to put a price on all greenhouse gases that play a significant role in trapping heat in the atmosphere through binding "minimum national standards" on the federal government and all of the provinces and territories of Canada.

For example, under Premier Blaine Higgs, the New Brunswick Attorney General submitted his intention to intervene in Saskatchewan's court challenge of the federal government's carbon pricing plan.

[b][20] On May 3, 2019, the Court of Appeal for Saskatchewan ruled in favour of the federal government in a 155-page 3–2 split decision that concluded that, "The Greenhouse Gas Pollution Pricing Act is not unconstitutional either in whole or in part.

[30][31] Specifically, writing for the majority, Chief Justice George Strathy ruled that the law was within federal jurisdiction "to legislate in relation to matters of 'national concern' under the 'Peace, Order, and good Government' [sic] clause of s. 91 of the Constitution Act, 1867.

"[27] Huscroft's dissent was described as "traditionalist" in its view of the division of powers and compared to Gérard La Forest, a former puis-ne on the Supreme Court of Canada, by former Attorney-General Peter MacKay.