A federal whistleblower complaint regarding an alleged "promise" made by President Donald Trump to a foreign leader has caused a showdown between Congress and the U.S. intelligence community, the Washington Post reported Wednesday night. According to the Post, Trump made a promise to a foreign leader, reportedly in a phone call this summer, "regarded as so troubling that it prompted an official in the U.S. intelligence community to file a formal whistleblower complaint with the inspector general for the intelligence community." It is unclear which foreign leader Trump may have been speaking to, but the Post reported that around the time in question, Trump communicated with the leaders of Russia, North Korea, Pakistan, Qatar and the Netherlands. The intelligence community's inspector general reportedly found the complaint credible and a matter of "urgent concern," a classification which triggers congressional notification. However, the Post reported that acting director of national intelligence Joseph Maguire has refused to share the complaint with lawmakers. The inspector general, Michael Atkinson, is scheduled to appear before a classified hearing with the House Intelligence Committee on Thursday.