Congress decides what laws to enact and Congress then decides what administrative agencies or executive departments to establish, to administer, and execute those laws. So, administrative agencies derive all of their powers from Congress, but those agencies are themselves contemplated in the Constitution. The Constitution says that the President may require the opinion in writing of his principal executive officers and that shows that the Constitution and the Framers explicitly contemplated that executive departments or agencies would form a part of the national government. And indeed executive departments and agencies have been with us since the beginning of the republic, since 1789, since President Washington's first administration. Even though administrative agencies are part of the executive branch, they raise questions as to whether they might be unconstitutionally structured. For example, agencies routinely issue rules and regulations and these seem to be a lot like legislation, legislative acts, but Congress under our constitutional system must be the one to exercise legislative power. As for executive power, sometimes Congress creates independent agencies whose officials are insulated from the president's ability to oversee, direct, and remove them. This seems to recreate a plural executive explicitly rejected by our Framers. Administrative agencies also routinely adjudicate disputes and sometimes issue hefty fines against private individuals. Well, these seem to be cases that historically should have been heard by Article Three courts and so there's a question as to whether administrative agencies sometimes violate the constitution's provisions for legislative, executive, and judicial power.