The United States has suspended funding for the Open Skies Treaty following the signing of a $717-billion national defense policy act into law by U.S. President Donald Trump on Monday.

The measure could have implications for Russia’s ability to conduct observation flights over the United States.

Under the 34-member treaty that entered into force in 2002, countries are allowed to conduct unarmed observation flights to promote openness and transparency of military forces and activities. Russian aircraft had reportedly last conducted reconnaissance flights over the U.S. in August 2017 — over the Capitol, the Pentagon, the White House and Bedminster, New Jersey, where Trump was taking a working vacation.

The 2019 U.S. defense policy act withholds funds for the Open Skies Treaty until Trump provides Congress assurances that Russia “is in complete compliance with its obligations" under the treaty.

Over the past year, Russia has cut the number of air bases the U.S. can observe after Washington accused Moscow of violating the treaty by limiting flights over the militarized Kaliningrad exclave in Europe.