The United States is once again imposing tariffs on some imported Canadian aluminum products and Canada is gearing up to retaliate with reciprocal tariffs.

Trudeau said he made that point to the U.S. president in a phone call earlier Monday.

Steve Verheul say that under the terms of the May 2019 agreement on tariffs, Canada would be able to impose retaliatory levies against American aluminum.

Under the new CUSMA agreement, Canada will provide U.S. dairy farmers access to about 3.5 per cent of its $16 billion annual domestic dairy market.

He said that the two leaders will instead talk by telephone later on Monday morning.

There's new conflict over aluminum. Precisely why remains a mystery to trade and industry insiders, although it's likely the result of COVID-19, international metals arbitrage, Russian-made aluminum and President Donald Trump's re-election campaign.

The revamped trade pact between the United States, Canada and Mexico taking effect on Wednesday was meant to create a kind of fortress North America, boosting the region's competitiveness -- but cracks are already starting to show in the foundation.

Andres Manuel Lopez Obrador has publicly urged Prime Minister Justin Trudeau to take part in the meeting, but Canada's government has given no indication yet that he will attend.

Despite repeated questioning last week, Canadian federal ministers refused to answer questions about whether they received notification of any such threat.

Transport Canada introduced the new rules last summer to meet the demands of an International Maritime Organization treaty that took effect in 2017 aimed at limiting the spread of harmful or invasive species.