House Foreign Affairs Committee Chairman Eliot Engel on Monday expressed his alarm over the Trump administration’s potential plans to pull out of the Open Skies Treaty, a post-Cold War agreement that allows countries to operate reconnaissance flights over other nations and collect data on military activities with the aim of building trust between countries. Since coming into force in 2002, the treaty has become a key tool for the U.S. and its European allies to monitor Russian military deployments to former Soviet satellite countries, including Russian aggression in Ukraine. Withdrawing from the treaty could upend this transatlantic alliance, and place Ukraine at greater risk.

Rep. Eliot Engel (D-NY), chairman of the House Committee on Foreign Affairs, sent a letter to National Security Adviser Robert O’Brien on Monday, expressing his alarm over Trump’s reported plans to leave the treaty. “I am deeply concerned by reports that the Trump Administration is considering withdrawing from the Open Skies Treaty and strongly urge you against such a reckless action... American withdrawal would only benefit Russia and be harmful to our allies’ and partners’ national security interests,” Engel wrote. “... The United States should prepare for the challenge that Russia presents—not abandon mechanisms that provide the United States with an important tool in maintaining surveillance on Russia.”