Canadian air traffic controllers have bought hundreds of pizzas for their American counterparts over the past few days in what has become an industry-wide show of support during the U.S. government’s partial shutdown.

Peter Duffey, the head of the Canadian Air Traffic Control Association, said the initiative began Thursday when employees at Edmonton’s control centre took up a collection to buy pies for controllers in Anchorage, Alaska.

Other facilities across Canada decided to join in, and the idea snowballed.

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“The next thing we knew, our members were buying pizzas left, right and centre for the colleagues in the U.S,” Duffey said Sunday in a phone interview.

“As it stands right now, I believe we’re up to 36 facilities that have received pizza from Canada, and that number is growing by the hour.”

Duffey estimates that as of Sunday afternoon, some 300 pizzas had been received by American controllers, many of whom took to social media to express their gratitude.

Duffey said many union members had been looking for a way to show solidarity with their American colleagues, who have been working without pay due to the partial shutdown.

“Air traffic control is a very stressful job,” he said.

“They say you have to be 100 per cent right, 100 per cent of the time. People just don’t need to be reporting to work with the added stress of worrying about how to pay their mortgages and grocery bills on top of it.”

He said one anonymous Canadian donor contributed $500 to the pizza fund, while another single-handedly bought lunch for two facilities in Phoenix, Arizona, to thank them for “taking care of all the snowbirds from Western Canada who go down for the winter.”

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Ron Singer, the national media manager for Nav Canada, which manages the country’s civil air navigation, says Canadian and American air traffic controllers interact “on a daily basis” as they manage North American airspace.

“There’s a bond there, automatically,” he said in a phone interview.

He said that as of Sunday afternoon, Nav Canada employees from all of Canada’s seven control centres and many of its towers have bought lunch for their U.S. counterparts.

Some 10,000 air traffic controllers in the United States have been working without pay since late December due to the ongoing government shutdown.

Their union filed a lawsuit in federal court in Washington on Friday, asking for an order compelling the government to pay them what they’re owed.