ST. STEPHEN, N.B. -- Prime Minister Justin Trudeau slammed New Brunswick Thursday for its opposition to the federal carbon levy, saying Conservative governments across the country "don't think that fighting climate change is a priority."

Trudeau made the comments in New Brunswick, one of four provinces where the federal carbon pricing backstop takes effect next week.

During a stop at the Garcelon Civic Centre in St. Stephen, Trudeau told reporters there needs to be a price on pollution.

"I regret that the government of New Brunswick doesn't think that putting a price on pollution is important," the prime minister said.

"It's the 21st century. We know climate change is real. We know that one of the challenges we have is that pollution has been free. We need to put a price on it."

Ottawa has promised to return all the funds collected in rebates to individuals, businesses, local governments and other organizations.

"We are doing that in a way that right now at tax time, New Brunswickers are going to be able to get money directly back, which will more than cover, for the vast majority of families, any extra expenses attached to the new price on pollution," said Trudeau.

"It's a shame that the Conservative governments, not just here, but across the county, don't think that fighting climate change is a priority. But I know New Brunswickers and indeed Canadians know that we have to do it if we're going to keep our economy strong into the future."

The federal carbon pricing backstop kicks in Monday in the four provinces that didn't have their own carbon pricing system -- Saskatchewan, Manitoba, Ontario and New Brunswick.

In a news release earlier this month, New Brunswick's Energy and Resource Development Minister Mike Holland was critical of the carbon levy.

"Any new tax, especially a carbon tax that will make everything you buy more expensive, is not the best approach to change behaviours and will only add unnecessary costs that hurt the economy and negatively affect New Brunswick families," he said.

"This federal carbon tax will unfairly burden New Brunswick's rural households, those families who heat homes with oil or gas, and those who do not have the option to drive less."

Earlier Thursday, Trudeau met with seniors in Halifax as he made a quick swing through the region to talk about pharmacare and the federal budget.

Trudeau also spoke with protesters concerned with a plan to store natural gas in huge underground caverns north of the city.

For the past 12 years, Alton Gas has been planning to pump water from the Shubenacadie River to an underground site 12 kilometres away, where it will be used to flush out salt deposits, and create up to 15 caverns. The leftover brine solution would then be pumped back into the river over a two- to three-year period.

Darlene Gilbert, an Indigenous woman who has been protesting the Alton Gas project for several years, told the prime minister she wanted Ottawa to take a stronger stance - and reject the project's plan under the Fisheries Act.

She told him adding salty water to the Shubenacadie is a clear case of depositing "deleterious substances" into waterways frequented by fish, which is prohibited under the Fisheries Act unless a federal exemption is applied.

"You're not protecting our waterways. ... You're telling us to brine and poison our waters so you guys can make energy," Gilbert said to Trudeau.

Trudeau waited for the protesters to complete their points and then asked for an opportunity to respond.

"We're going to work with local communities. We're going to work with the chiefs, we're going to work with the provincial government. ...We're going to work with the grandmothers. We're going to work with the community to move forward on regulations in a way that addresses your concerns," he said.

"I very deeply respect your position on this as a grandmother. I do. My responsibility is to work with everyone and listen to everyone and make the right decision for the community," he said.

The federal government said last month that it will step in to regulate the company's plan in a way that would manage potential threats to fish, fish habitat and human health.