President Trump called on the Senate Monday to take up a bill to curb shipments of illicit fentanyl through the U.S. postal system, and also drew attention to the outsize role that the powerful painkiller is playing in overdose deaths.

“It is outrageous that Poisonous Synthetic Heroin Fentanyl comes pouring into the U.S. Postal System from China,” Trump tweeted on Monday. “We can, and must, END THIS NOW!”