A bipartisan group of five lawmakers are urging Defense Secretary Chuck Hagel to stop buying Mi-17 helicopters from Russian arms company Rosoboronexport, in light of Russia’s moves to annex the Ukrainian peninsula of Crimea.

“Given Russia’s recent actions that violate the sovereignty and territorial integrity of Ukraine, including its support of the illegal referendum for Crimean separation, we strongly urge you to terminate these contracts,” said the letter.

The U.S. purchases the Russian Mi-17 helicopters for the Afghan air force, which officials argue are sturdy and simple workhorses that are suitable for Afghanistan’s thin air and challenging terrain.

The lawmakers, led by Congresswomen Rosa DeLauro (D-Conn.) and Kay Granger (R-Tex.), said canceling the contracts was in Hagel’s authority, since it goes against U.S. interests and met criteria under an executive order the president signed on Monday.