Tensions have been brewing between the United States and Canada ever since President Trump ignited a trade war with U.S. neighbors — and now, they’re spilling over into the world of sports.

On Sunday, the NBA’s Toronto Raptors hosted the Los Angeles Clippers. But before the game began, fans at the Scotiabank Arena loudly booed during the U.S. national anthem.

The jab was immediate once 15-year-old Kyra Daniel, who is from Ontario, Canada, started singing “The Star-Spangled Banner.” It largely died down halfway into the performance, but some consistent booing remained, says Adam Laskaris, a sports journalist who attended the basketball game.

Daniels received resounding applause after singing “O’ Canada,” the Canadian national anthem.

Similar jeers broke out at National Hockey League games in Canada over the weekend, including during performances of “The Star-Spangled Banner” before matches between the Ottawa Senators and the Minnesota Wild on Saturday night and between the Vancouver Canucks and the Detroit Red Wings on Sunday.

Laskaris, who works at Daily Hive, a Canadian online news outlet, told NPR that he believes the boos were a direct response to the tariffs imposed by Trump. On Saturday, the U.S. president signed executive orders imposing a 25% tax on most imports from Canada and Mexico, and a 10% tax on goods from China. The tariffs are set to go into effect on Tuesday.

“We’ve always had a pretty friendly relationship with the U.S. in my lifetime, and this feels different,” he said. “I think a lot of us just feel betrayed more than anything given the history of the two countries almost always supporting one another.”

In turn, Canada’s government said it would impose 25% retaliatory tariffs on a range of U.S. products, including appliances, clothing, wine and spirits, orange juice, peanut butter and motorcycles. The Canadian tariffs are also scheduled to take effect on Tuesday.