Air traffic controllers in Canada have bought air traffic controllers in the U.S. hundreds of pizzas in recent days to show support for their counterparts in what is now the longest government shutdown in U.S. history.

The head of the Canadian Air Traffic Control Association (CATCA) said the idea took root on Thursday when employees at a control center in Edmonton, Alberta, decided to buy pizza pies for controllers in Anchorage, Alaska — nearly 2,000 miles away.

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Staff at other control facilities across Canada decided to join in, and the idea snowballed.

"The next thing we knew, our members were buying pizzas left, right and center for the colleagues in the U.S," Peter Duffey, of CATCA, told The Associated Press. "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."

Some 10,000 air traffic controllers in the U.S. have been working without pay due to the partial government shutdown, which began on Dec. 22.

Duffey said that as of Sunday afternoon, around 300 pizzas had been received by American air traffic controllers.

Controllers from both countries interact "on a daily basis" and have "a bond there, automatically" as they manage North American airspace, Ron Singer, the national media manager for Nav Canada, said.

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The role of an air traffic controller is widely considered to be a demanding job. Duffey said the job is "very stressful," as "you have to be 100 percent right, 100 percent 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.

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About 800,000 federal workers missed paychecks on Friday amid the partial shutdown. The House and Senate recently voted to give them back pay whenever the federal government fully reopens.

The Associated Press contributed to this report.