Donald Trump said if NATO partners do not ante up their fair share of defense spending the US may not come to their aid. Since his campaign Trump has insisted US help would be conditional on whether or not NATO members met their financial obligations.

US Secretary of State Rex Tillerson put pressure on NATO leaders Friday in Brussels.

Tillerson warned NATO members that they need to come up with the money or with a clear plan on how they intend to reach their pledged goal of two percent of their gross domestic product before Trump meets with them in May.

“Our goal should be to agree at the May leaders meeting that by the end of the year all allies will have either met the pledge guidelines or will have developed plans that clearly articulate how, with annual milestone progress commitments, the pledge will be fulfilled,” Tillerson said.

Tillerson made no suggestions about what would happen if the goals set forth were not met, but Trump has suggested the US might not come to their defense of allies who didn’t do their fair share, a signal that worries allies near Russia due to the Communists state’s recent militarily aggression.

The German Foreign Minister Sigmar Gabriel said the US demands are “unrealistic ,” and that his country alone would have to increase spending from $35 to $37 billion. “I don’t know a politician in Germany who believes that this would be achievable or even desirable,” he said.

In addition to Germany’s dislike for the increased spending other nations would have to ante up much more. Canada, Italy and Spain would need to nearly double their current spending to reach the demand of the Trump Administration.

The Trump Administration has also criticized NATO members for not doing more to fight ISIS.

NATO Secretary General Jens Stoltenberg said NATO learned lessons from Afghanistan, Kosovo and Bosnia-Herzegovina that deploying troops in such places is not good for NATO, but they do feel they are doing their share in fighting terrorism by training forces and building security institutions.

The North Atlantic Treaty Organization was formed in 1949. NATO constitutes a collective defense, whereby it member states agree to a mutual defense response in case any member comes under attack, but Trump’s rhetoric is making NATO members uneasy about US demands and intentions.