Ontario's top court rules today on the validity of the federal government's carbon charge.
The Doug Ford government challenged the constitutionality of the carbon-pricing law before a five-judge panel in April.
It argued the Liberal government under Prime Minister Justin Trudeau overstepped its authority in imposing the charge.
For its part, Ottawa argued climate change poses an urgent threat and is an issue of national concern.
The federal government says its approach respects provincial jurisdiction.
Last month, the Saskatchewan Court of Appeal sided with Ottawa in a similar challenge.