Automakers have temporarily closed factories in the United States and Canada after truck drivers protesting Covid-19 vaccination mandates blocked critical border crossings, cutting off the flow of auto parts and other goods between the countries.

The Freedom Convoy protests, which converged last month in Ottawa, Canada’s capital, spread to the Ambassador Bridge that connects Detroit in the United States and Windsor, Ontario, where traffic was blocked for a fourth day on Thursday .

The disruptions illustrated how protests have exploded in recent weeks beyond Canada’s borders and affected trade with its North American neighbor and biggest trading partner.

The coronavirus pandemic has made supply chains prone to disruption and automakers have warned that protests could further exacerbate component shortages that have plagued them in recent months.

General Motors said its Lansing, Mich. plant, which makes Chevrolet and Buick SUVs, canceled its second shift Wednesday and its first and second shifts Thursday due to parts shortages. GM said it was working with suppliers to mitigate the situation.

Toyota halted production at its three Canadian plants and one plant in Kentucky, saying it expected the disruptions to last through the weekend. The Kentucky plant, Toyota’s largest in the world, manufactures models such as the RAV4 crossover and the Camry sedan.

Ford, which was operating two plants in Ontario at reduced capacity on Thursday, warned that supply chain bottlenecks between the United States and Canada “could have a widespread impact on all automakers” if the disruption was not resolved quickly.

“This Detroit/Windsor Bridge disruption is hurting customers, autoworkers, suppliers, communities and businesses on both sides of the border who have already been experiencing parts shortages for two years as a result of the global semi- drivers, Covid and more,” Ford said.

Stellantis, whose brands include Fiat, Jeep and Ram, said while all of its North American plants were operating, some in the United States and Canada cut their second shifts short Wednesday night due to “parts shortages caused by the closure of Detroit/Windsor Bridge”.

“The situation at the Ambassador Bridge, combined with an already fragile supply chain, will bring further hardship to people and industries still struggling to recover from the Covid-19 pandemic,” Stellantis said in a statement.

The Biden administration on Thursday urged the Canadian government to use its federal powers to end the truck blockade. The White House said Alejandro Mayorkas, secretary to the secretary of homeland security, and Pete Buttigieg, secretary of transportation, spoke with their Canadian counterparts and urged them to help resolve the standoff.

“U.S. and Canadian border and customs officials are working urgently to ensure the continued flow of goods and services across our international border, taking advantage of alternate land routes, as well as air and sea options,” said the White House in a statement.

Trucks heading to Canada encountered traffic jams after being diverted from the Ambassador Bridge to the Blue Water Bridge in Port Huron, Michigan © Mandi Wright/Detroit Free Press/AP

The U.S. Chamber of Commerce, National Association of Manufacturers and Business Roundtable released a joint statement on Thursday calling for a resolution to the border disruption, which it said ‘added to significant supply chain tensions manufacturers and other businesses”.

Marco Mendicino, Canada’s federal public safety minister, said police reinforcements were being sent to Windsor and Coutts, Alberta.

More than $300 million worth of goods crosses the Ambassador Bridge every day, roughly a quarter of all trade between the United States and Canada.

Edward Alden, senior fellow at the Council on Foreign Relations, said the bridge was “the greatest commercial thoroughfare in North America”.

“More trade passes through this bridge than through any other crossing, it is the most important route,” Alden added. The automakers’ “just-in-time” manufacturing process meant they were particularly hard hit by any delays in receiving parts, he added.

“Everything is set up for them assuming it will be easy to come and go on that bridge,” he said.

The crossing was not technically closed to U.S.-bound traffic on Thursday, according to Windsor police, but protesters were “making it difficult to get to the bridge.” Police have warned of “significant” delays.

The US Department of Homeland Security said it was following reports of a potential convoy that may be planning to visit several US cities.

The Ambassador Bridge traffic jam put pressure on Canadian Prime Minister Justin Trudeau, who called the protests “unacceptable” and warned of the impact on manufacturers. “We must do everything to end it,” he said.

However, Trudeau remained firm in his support for Covid restrictions, including the vaccination mandate for cross-border truckers that sparked the Freedom Convoy.

Matt Moroun, president of the Detroit International Bridge Company which controls the Ambassador Bridge, called on the Canadian government to end the protest by repealing the vaccination mandate or removing vehicles blocking access to the crossing.

“We are all just beginning to feel the devastating impact,” Moroun said. “This can not go on.”

The Canadian Trucking Alliance said 90% of drivers have been vaccinated against Covid. This week, the group urged government officials to “work together to end the current lockdowns immediately”.

Parts of Canada began lifting Covid rules after a drop in reported infections, which had been driven by the spread of the Omicron variant.

Alberta ended its vaccine passport program and capacity limits on public places on Tuesday, with Conservative Premier Jason Kenney saying the threat to public health from Covid “no longer outweighs the hugely damaging impact health restrictions on our society”.

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