As the United States agreed Friday to lift steel and aluminum tariffs on Canada, some of Canada's Official Opposition Conservatives welcomed it as "good news," but warned of "risk."

"The US can re-impose tariffs if (Canadian) imports surge 'meaningfully' beyond historic volumes," said Conservative Shadow Minister of Foreign Affairs Erin O'Toole and Shadow Minister for International Trade Dean Allision in a statement.

"The term 'meaningful' is left undefined and this could lead to difficulties in the future," they added.

According to the joint US-Canada statement released Friday, "In the event that imports of aluminum or steel products surge meaningfully beyond historic volumes over a period of time, with consideration of market share, the importing country may request consultations with the exporting country."

Following that, the importing country "may impose duties of 25 percent for steel and 10 percent aluminum in respect to the individual product(s) where the surge took place." It is to be based on individual product categories, but not on the entire steel or aluminum industry.

If it happened, the exporting country agrees to retaliate only in the affected sector, such as aluminum and aluminum-containing products or steel, said the agreement.

With the tariffs off the table, Canadian Prime Minister Justin Trudeau signaled on Friday that Canada could proceed with finalizing the new North American free trade deal, known in Canada as the Canada-United States-Mexico Agreement.

On Friday, US Vice President Mike Pence tweeted that he would be in Ottawa on May 30 to meet with Trudeau on "advancing" that pact "as swiftly as possible."

On June 1, 2018, the United States slapped a 25-percent tariff on Canadian steel imports, and a 10-percent tariff was imposed on its aluminum imports through a rarely used national security provision under US trade law.