OTTAWA — The Canadian Auto Workers Union warns that if "economic disruptions" planned for Wednesday escalate to full-on blockades, the economy could indeed be brought to its knees.

First Nations groups behind the Idle No More movement have planned major disruptions at corridors across the country including highways, railways and border crossings, in what they call a "Day of Action" to protest environmental legislation and lack of respect for treaties.

While some chiefs have called for peaceful protests and have urged activists to respect the law, others have taken a harder line.

Grand Chief of the Manitoba Chiefs Derek Nepinak last week threatened to "bring the Canadian economy to its knees."

One target is the Ambassador Bridge, North America's busiest border crossing, connecting Windsor, Ont., to Detroit, Mich. Each year, 25 million people cross the bridge and more than $130 billion in goods are transported across it.

Ken Lewenza, president of the CAW, told QMI Agency that if the "disruption" planned for the bridge turns into a full blockade or goes on for longer than four hours, it "could shut down production" at auto and truck plants.

"It's safe to say that anything beyond four hours would definitely create the potential for lost production in Canadian assembly plants," he said. "We're talking about 40- to 50,000 employees here. So there's no question that any kind of delay, even if it doesn't shut down an assembly plant, would create significant financial consequences."

Auto-manufacturing plants use a just-on-time policy, meaning parts arrive at a given plant on the same day they are to be assembled.

The good news, Lewenza said, is that the biggest plant - Windsor Chrysler - will be closed Wednesday for inventory.

Sgt. Matthew D'Asti with the Windsor police said his force will closely monitor protests and decisions will be made Wednesday whether to arrest any individuals breaking the law.

"Our main priority is to keep people safe, including the protesters," he said.

Because Idle No More has no central organization, it is difficult to determine every site targeted for protest, but actions this weekend focus on major routes including Hwy. 63 to Fort McMurray, Alta., and routes near Calgary's Bow River.

Asked what the government is doing to prevent significant economic disruptions from taking place, the Canada Border Services Agency replied that "it will be business as usual at all of CBSA ports of entry."

"We will update travellers should there be service interruptions or longer wait times, as per our usual protocol," CBSA spokeswoman Jean D'Amelio Swyer said.