Shares of pharmaceutical companies were under pressure ahead of Monday’s open after President Donald Trump said he will sign an executive order to slash prescription-drug prices.

In a post on his Truth Social platform on Sunday, Trump said the order, to be signed at 9 a.m. Monday, will institute a “most favored nation” policy where the U.S. will pay the same price for prescription drugs and pharmaceuticals “as the nation that pays the lowest price anywhere in the world.”