Prime Minister Justin Trudeau will attend the North Atlantic Treaty Organization summit in Brussels next month amid escalating tensions between him and U.S. President Donald Trump. 

Trudeau formally announced Monday that he will attend the summit on July 11 and 12, where he plans to discuss “trans-Atlantic security issues and challenges with other NATO leaders.”

Weeks ahead of the summit, Trump sent Trudeau a letter calling on Canada to increase its defence spending on NATO.  The Canadian Press reported that Trump’s letter expressed “growing frustration” in the U.S. over what Trump perceives to be a lack of defence spending by NATO allies. 

In the past, Trump has publicly berated NATO allies for not increasing their spending. More recently, he has attacked Trudeau and Canada in an ongoing trade spat, after slapping tariffs on Canadian steel and aluminum. Over the weekend, Trump also threatened “reciprocity” against trade partners who have imposed or are planning to impose retaliatory tariffs on U.S. goods.

At the Brussels summit, NATO leaders are expected to discuss modernization of the alliance and NATO’s relationship with Russia, among other topics.