This is well within the president's powers under existing law. If Congress disagrees, they can always supersede. This isn't even close to legislating. Look at

This is well within the president's powers under existing law. If Congress disagrees, they can always supersede. This isn't even close to legislating. Look at some recent Supreme Court decisions and the amount of latitude federal agencies have, if you want to see something more closely resembling legislation from outside of Congress.