The anti-vaccination trucker protest that has paralyzed the Canadian capital, Ottawa, has spread to Michigan’s border and threatens to create chaos in an auto industry already struggling to cope with what industry experts have described as a “fragile supply chain.”

Demonstrators have been setting up blockades at the two bridges linking Ontario and Michigan since Monday. The Blue Water and Ambassador bridges together serve thousands of trucks every day, many of them carrying automotive parts and finished vehicles.

Traffic over the Ambassador Bridge has come to a virtual halt. Only a small number of trucks moved from Canada to Michigan on Wednesday. The situation at the Blue Water Bridge connecting Sarnia, Ontario, to Port Huron, Michigan, isn’t much better, with reported delays of at least 4½ hours.

On Wednesday, the Chrysler Pacifica minivan plant became the first direct casualty. Officials with the leading global automaker Stellantis temporarily halted production at the factory because it doesn’t have enough parts. Ford on Wednesday became the second manufacturer to take steps to deal with parts shortages. 

“While we continue to ship our current engine inventory to support our U.S. plants, we are running our plants at a reduced schedule today in Oakville [Ontario] and our Windsor engine plant is down,” Ford said in a statement.

General Motors, Detroit’s largest automaker, confirmed late on Wednesday that it had temporarily cut the second shift at a plant in Lansing, Michigan producing SUVS for the Buick, Chevrolet and GMC brands.

It could be a matter of hours before other automakers, domestic and foreign, have to take steps at assembly and parts plants within hours of the two bridge crossings.

“Blockades at Canada’s borders are threatening fragile supply chains already under pressure due to pandemic related shortages and backlogs,” Brian Kingston, the CEO of the Canadian Vehicle Manufacturers’ Association, said in a statement.

“We are calling on cooperation from all levels of government to resolve this situation and bring an immediate end to these blockades.”

Truckers have been tying up traffic in Ottawa since last month, protesting mask and vaccination mandates. Prime Minister Justin Trudeau decried the demonstrations this week, insisting the protesters are “trying to blockade our economy, our democracy and our fellow citizens’ daily lives.”

“It has to stop,” Trudeau said. But, if anything, the protest has spread, and on Monday, a vanguard group began blockading access to the Ambassador Bridge, which links Windsor, Ontario, to Detroit.

Within hours, authorities on both sides of the border declared the route closed. That quickly created a logistics nightmare. The span, which opened in November 1929, today serves about 2.5 million trucks annually, according to the Windsor-Detroit Bridge Authority. It handles about $100 billion in cross-border shipments of automotive parts and fully assembled vehicles. The Ambassador Bridge alone accounts for an estimated 20 percent of all U.S.-Canadian trade.

Officials on the Windsor side of the bridge have been struggling to open up access to the Ambassador Bridge and had only partly succeeded as of Wednesday morning, with a small flow of traffic trickling over to Michigan from the Canadian side. 

Authorities began redirecting traffic to two other routes linking Michigan and Ontario. Passenger traffic between Windsor and Ontario has been heavier than normal but is moving through the Detroit-Windsor tunnel. But the route under the Detroit River can’t handle large trucks. They’ve had to head north to the Blue Water Bridge.

Protesters began moving to tie up that route on the Canadian side Tuesday. Combined with the added traffic load diverted from the Ambassador Bridge, reports from border officials indicate that it is taking at least four hours for trucks to cross the twin spans linking Sarnia, Ontario, and Port Huron, Michigan. That’s on top of the added travel time to and from the Blue Water Bridge.

The industry has been struggling since the beginning of the Covid-19 pandemic and the three-month shutdown of production that was ordered in the spring of 2020. Since then, manufacturers have faced not only manpower issues, but also an ongoing shortage of semiconductor chips. Ford this week was forced to suspend or cut back production at eight North American assembly plants because of a lack of chips. A number of those plants are within an hour of the Ambassador Bridge and also depend on some Canadian-made parts.

“Basically if there’s a shutdown of transportation routes, the auto industry comes to a screeching halt in about two days,” Robert Wildeboer, the executive chairman of the parts supplier Martinrea International, told BNN Bloomberg Television on Tuesday.

Consumers would quickly feel the impact. They’ve already found it difficult to buy the vehicles they want, said Tyson Jominy, a senior analyst with J.D. Power. The research firm estimated that there were barely 1 million vehicles on U.S. dealer lots in January. Normally, there are more than 3 million this time of year.

The shortages have been a factor in a sharp run-up in the cost of a new car, which, on average, reached $45,000 to $47,000 in December, according to J.D. Power, the auto sales and analysis site Edmunds and other tracking services.