This weekend, Canada will start requiring long-haul truckers crossing the border from the U.S. to show proof they’ve been vaccinated against COVID-19.

The mandate marks a departure from pandemic policy until now.

During the pandemic, even during periods of lockdown and border closures, truck drivers have been able to cross the U.S.-Canada border with ease, thanks to their classification as essential workers. That’s about to change.

Stephen Laskowski, president and chief executive of the Canadian Trucking Alliance, said once the vaccine mandate for truck drivers takes effect on Saturday, as many as 16,000 unvaccinated drivers could be sidelined.

“We need more truck drivers in Canada and the United States whether it’s domestic or crossing the border – not less,” he said.

Laskowski said his association needs more time to convince vaccine hesitant truck drivers to get the jab.

Canada’s government has so far resisted pressure to reverse itself.

The stakes are high, said operations professor Fraser Johnson of the Ivey Business School in London, Ontario, as $1.5 billion worth of goods cross that border each day.

“Broadly speaking, it’s going to increase the costs of transportation. It’s going to create delays,” he said.

In other words, more constraints on an already challenged supply chain.