Prince Edward Island and Quebec have petitioned to become interveners in Saskatchewan's legal challenge of the federal carbon tax.

P.E.I.'s Progressive Conservative Premier Dennis King says he does not want to be seen as a Progressive Conservative premier joining the "resistance" of other conservative provincial leaders across the country fighting the Trudeau government's carbon tax.

He says P.E.I. is joining the court challenge simply because he wants his province to have the chance to speak up in court, if necessary - possibly even to support the tax.

King met Justin Trudeau today in Ottawa and says he told the prime minister he's in favour of the federal Liberals' carbon-pricing program, but also wants to find ways to reward carbon-reduction measures rather than just penalizing emitters and consumers.

Quebec Justice Minister Sonia LeBel also says in a statement today her province is intervening in the Saskatchewan case to ensure Quebec retains its jurisdictional autonomy over its cap-and-trade system.

Quebec and P.E.I. are among seven provinces now registered as interveners in the Saskatchewan challenge to the Supreme Court of Canada, which has previously failed at the province's Court of Appeal.