Attorney General Jeff Sessions on Wednesday called Senate Judiciary Committee Chairman Chuck Grassley’s latest sentencing reform legislation a “grave error,” saying it would lighten sentences for dangerous drug traffickers.

“In recent years, convicted drug traffickers and other violent criminals have received significant sentencing breaks from the federal courts and the United States Sentencing Commission,” Sessions wrote in a letter to Grassley. “Passing this legislation to further reduce sentences for drug traffickers in the midst of the worst drug crisis in our nation’s history would make it more difficult to achieve our goals and have potentially dire consequences.”