From The Truth About Guns:

Administrative agencies, like the ATF and EPA, are increasingly encouraged to write their own rules far beyond the scope that the law allows. Hence why you saw “bump stocks” banned without Congress acting, why you saw 7N6 ammunition disappear, why you saw foreign made semi-autos dry up. None of this came with the help of Congress. All of it came at the behest of the executive branch, headed up by none other than whoever was president at the time.