A blacken flag at the CN blockade near Sarnia, Ont. (HEATHER WRIGHT/QMI AGENCY)

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.