Three Democratic senators are demanding that Secretary of State Marco Rubio reject what they characterized as a scheme to withhold lifesaving HIV treatment from over a million Zambians unless the African nation agrees to grant US businesses favorable access to its copper mines.

Jeanne Shaheen, the top Democrat on the Senate Foreign Relations Committee, along with Sens. Chris Coons, D-Del., and Brian Schatz, D-Hawaii, wrote in a letter to Rubio that they are “alarmed by reports” about State Department officials proposing to condition both HIV funding and previously pledged Millennium Challenge Corporation economic assistance on Zambia agreeing to favorable economic reforms for US businesses.

“We urge you to reject this tactic of economic coercion,” they wrote in the Thursday letter, which was shared first with Semafor.

It follows reporting from The New York Times that State had crafted a plan to pressure Lusaka on mining policy by threatening to end health support “on a massive scale.” The senators called the reported approach “a disturbing break from the long held bipartisan support for PEPFAR,” a program that has enjoyed rare bipartisan backing in Congress.