Trump has now preposterously upped the demand, insisting that every member nation pay 4 percent of its GDP on defense - an amount the USA doesn't even live up to.
Trump said he made his anger clear to allies on Wednesday.
"I read the 140-character messages", Macron said.
"Trump wants to see our allies share more of the burden and at a very minimum meet their already stated obligations".
Striking a strident tone at the summit, Trump's aspirational target of 4 percent of gross domestic product (GDP) was above the United States own spending on defense.
Earlier Thursday, Trump called out USA allies on Twitter as he attended a second day of meetings with leaders of the military alliance.
Trump's late tweet also repeated his insistence from earlier in the summit that Germany was wrong to support an $11 billion Baltic Sea pipeline to import even more Russian gas while being slow to meet targets for North Atlantic Treaty Organisation spending.
The U.S., which spent $685.9 billion on defense in 2017, now makes up 51.1 percent of NATO's combined GDP.
Trump first attacked the alliance as "obsolete" during the 2016 presidential campaign, and he has continued maligning American allies in office.
"Presidents have been trying unsuccessfully for years to get Germany and other rich NATO Nations to pay more toward their protection from Russia", Trump wrote.
"We're protecting everybody, and yet we're paying a lot of money to protect", Trump said. In the afternoon, he heads to his next stop: the United Kingdom.
Reuters contributed reporting to this article. And "they have pledged to spend more". "It's really extraordinary that Donald Trump has to be the person to point out that the emperor in Europe has no clothes".
"I am very happy that today we are united in freedom, the Federal Republic of Germany", Merkel added.
U.S. President Donald Trump, left, and German Chancellor Angela Merkel pose for a photograph prior to a bilateral meeting on the eve of the G-20 summit in Hamburg, northern Germany, Thursday, July 6, 2017.
But Trump's belligerent statesmanship, together with the actions of his soulmate, Russian President Vladimir Putin, could well lame it forever. "But in each of the last 4 years, the vast majority of European nations in the alliance have increased their defense spending as percentage of GDP". "But it could lead to productive - something very productive, and maybe it's not".
"I have to tell you that the atmosphere last night at dinner was very open, was very constructive and it was very positive, " Kolinda Grabar-Kitarovic, the president of Croatia, told reporters.
"I think he has to expect they're going to deny, deny everything", the South Dakotan said.
As Trump made these comments, reporters at the scene noted that Kelly looked fairly uncomfortable.
Trump's next stop will be London, where he'll be meeting with Queen Elizabeth II and British Prime Minister Theresa May.
Woody Johnson, the USA ambassador to the United Kingdom, dismissed the significance of the protests, telling Fox News that one of the reasons the two countries are so close "is because we have the freedoms that we've all fought for".