Explaining NATO’s Article 4 as Estonia seeks consultations over Russian airspace violationEstonia has invoked NATO's Article 4 after Russian jets violated its airspace, prompting urgent consultations among allies. Estonia has requested consultations under Article 4 of NATO’s founding treaty. Article 4 puts urgent matters on NATO’s agendaArticle 4 is the shortest of the Washington Treaty’s 14 articles. Poland first invoked Article 4 on March 3, 2014, “following increasing tensions in neighbouring Ukraine, as a result of Russia’s aggressive actions,” according to the NATO website. In other words: Article 4 can be invoked without triggering Article 5, and vice versa,” he said.