The Supreme Court of Canada has postponed until at least June hearing a constitutional challenge of the federal government's carbon tax.

The top court was to have heard the challenge, launched by Saskatchewan and Ontario and supported by several other provinces, next week.

But, as part of a country-wide effort to stem the spread of COVID-19, Chief Justice Richard Wagner says the court is putting off several hearings, including on the much anticipated carbon tax case.

The top courts in Ontario and Saskatchewan rejected arguments by those provinces that the federal government doesn't have the constitutional authority to impose a carbon tax in provinces that don't impose a carbon price that meets federal standards.

They are appealing those rulings to the Supreme Court.

Wagner says the hearings on those appeals are being tentatively postponed until June, among other measures to reduce the potential for spreading COVID-19, including closing the Supreme Court building to visitors.

However, he says he'll continue to monitor the rapidly evolving health crisis and work on contingency plans.

The Saskatchewan government said it understands the need for the delay.

"While we look forward to challenging the federally imposed carbon tax at the Supreme Court of Canada, we agree that it is appropriate to postpone the case during the COVID-19 pandemic," Jim Billington, Premier Scott Moe's press secretary said in an email.

"Our government will remain focused on limiting the spread of COVID-19 in Saskatchewan."

Alberta is also challenging the carbon tax; it's top court last month agreed with the province that the tax is unconstitutional.

The court delay will also affect the hearing in a case involving a bid by the Toronto Star to stop the sealing of documents related to the estates of Toronto couple Barry and Honey Sherman, who were killed inside their Toronto mansion in December 2017.