Quebec and Prince Edward Island will act as interveners when Saskatchewan takes its federal carbon tax challenge to the Supreme Court of Canada.
It will be heard on December 5.
Both Quebec and P.E.I say they want to mention their own carbon pricing systems.
Other province’s challenging the federal government’s carbon tax are Manitoba and Alberta.
Ontario did as well, but its highest court decided in late June that the carbon tax is constitutional – the same ruling Saskatchewan’s Court of Appeal made in May.