AsianFin -- U.S. President Donald Trump said he would slash prescription drug prices by as much as 80% through a new policy tying U.S. costs to the lowest prices globally, a move that sent pharmaceutical shares tumbling across Europe and Asia on Monday.

In a social media post, Trump said he plans to sign an executive order at 9 a.m. Monday in Washington implementing a “most-favored nation” pricing model. While specific details were not provided, the announcement triggered investor concern over the potential impact on the world’s largest pharmaceutical market.

Under the proposed plan, Americans would pay no more than the lowest drug price available in any country, Trump said. He predicted this could cut U.S. drug costs by 30% to 80%, though acknowledged prices elsewhere may rise “to equalize,” adding the change would “finally bring FAIRNESS TO AMERICA!”