(CNN) Canadian air traffic controllers have been sending more than just radio signals across the border this weekend. They ordered hundreds of pizzas for their American counterparts working without pay due to the ongoing US government shutdown.

Huge thank you to our Union brothers and sisters at @CATCA5454 YYZ Tower for sending us pizza last night!! #NATCA #CATCA #unionstrong pic.twitter.com/S6erEK6FpG — NATCA EWR (@NATCAEWR) January 13, 2019

Peter Duffey, president of the Canadian Air Traffic Control Association, said the controllers were looking for a way to help the American controllers as they faced their first payday with no pay on Friday. On Thursday, one of CATCA's control centers in Edmonton, Alberta, had the idea of sending pizzas to the controllers in Anchorage, Alaska. The units are so close that they regularly interact and the Canadian controllers thought it would be a nice gesture of solidarity.

The idea took hold, and other units along the border sent pizza to the controllers with whom they share airspace. But now, Duffey said, units have been randomly selecting other units to send pizza to, sometimes based on similarities they think they share. Fort McMurray, for example, a unit in Alberta, chose to buy pizzas for a unit in El Paso, Texas, because it is also an oil town. Since Thursday, more than 350 pizzas have been sent to 49 FAA units across the United States and Duffey said the number is likely to grow.

Duffey said the response from the American controllers has been "very, very heartwarming." He said there have been instances when pilots have checked in to Canadian airspace and greeted their Canadian colleagues over the radio with messages of thanks on behalf of the controllers.

"In the big scheme of things, sending some pizzas to people that are missing paychecks is a small gesture," Duffey said, "but the message that it sends them is a big gesture."

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