TORONTO -- A law mandating that gas stations display anti-carbon tax stickers "furthers the purposes of freedom of expression," the Ontario government argues as part of its defence to a constitutional case.

The Canadian Civil Liberties Association is challenging the law, saying it violates free speech provisions because it constitutes compelled political speech. The government's statement of defence, which the CCLA posted on its website, argues that the suit should be dismissed.

It says the CCLA doesn't have standing to bring the challenge because it isn't a gas retailer and therefore isn't affected by the law.

The government also argues that the law does not limit the ability of gas stations to express any message or political speech.

"The (law) furthers the purposes of freedom of expression, which include seeking and attaining truth and participating in social and political decision-making, by promoting informed consumer choice and transparency," the government argues.

The stickers show the federal carbon tax adding 4.4 cents per litre to the price of gasoline now, rising to 11 cents per litre in 2022. They do not include information about rebates available to Ontario residents.

The stickers became mandatory shortly before the federal election campaign began in September.

"This is a tax on everything, and we're not going to stand for it," Energy Minister Greg Rickford told the legislature in April. "We're going to stick it to the Liberals and remind the people of Ontario how much this job-killing, regressive carbon tax costs."

The carbon tax is expected to cost a typical household $258 this year and $648 by 2022. Residents of provinces with the tax will be getting rebates on their income tax returns that start at $128 annually and increase for people with spouses or dependents at home.

Ontario is among several provinces challenging the constitutionality of the federal carbon tax in court. Premier Doug Ford said in August that voters would decide the fate of the province's legal challenge, but his government is nonetheless pressing ahead with an appeal to the Supreme Court of Canada. The province lost at the Ontario Court of Appeal in June.

This report by the Canadian Press was first published Oct. 30, 2019.