Three Republican senators are urging the Drug Enforcement Administration (DEA) to reject the top federal health agency's marijuana rescheduling recommendation, arguing that it would put the U.S. out of compliance with international treaty obligations and make it harder to ensure that other countries continue to enforce drug laws, "including for deadly narcotics like fentanyl."

In a letter sent to DEA Administrator Anne Milgram on Wednesday, Sens. Mitt Romney (R-UT), James Risch (R-ID) and Pete Ricketts (R-NE) said the agency should adhere to precedent and decline to move cannabis from Schedule I to Schedule III under...