Staying true to President Donald Trump’s rhetoric on the North Atlantic Treaty Organization, Defense Secretary and top Pentagon official Jim Mattis told member countries assembled in Brussels Wednesday they must increase defense spending or the U.S. will “moderate its commitment,” the Associated Press reported.

Mattis, who spoke before the 27 other member nations for the first time since he was confirmed, was relaying Trump’s decree that many NATO countries weren't paying “their fair share” when it comes to defense spending. NATO has served as a major military alliance between North American and European countries since 1949, following World War II.

“I owe it to you all to give you clarity on the political reality in the United States and to state the fair demand from my country’s people in concrete terms,” Mattis said in a closed-door meeting, according to the Washington Post. “America will meet its responsibilities, but if your nations do not want to see America moderate its commitment to the alliance, each of your capitals needs to show its support for our common defense.”

NATO members have been asked to shell out a minimum of 2 percent of their gross domestic product to defense spending, but most of the body has failed to do so in recent years.

“No longer can the American taxpayer carry a disproportionate share of the defense of Western values,” Mattis said. “Americans cannot care more for your children’s security than you do. Disregard for military readiness demonstrates a lack of respect for ourselves, for the alliance and for the freedoms we inherited, which are now clearly threatened.”

Aside from the U.S., only Estonia, Greece, Poland and the United Kingdom have allocated the pledged 2 percent. The U.S. and UK have much stronger economies than the other three, but well-oiled economic powers like France and Germany were failing to meet the requirement.

Mattis’ remarks could be disconcerting to other NATO members considering Russia’s increased military activity in recent years. President Vladimir Putin’s military already annexed Crimea from the Ukraine and has positioned missiles and troops in areas that have worried much of Europe.