U.S. Constitution Series, Article I, Section 1.

Section 1 - The Legislature

All legislative Powers herein granted shall be vested in a Congress of the United States, which shall consist of a Senate and House of Representatives.

This is actually far more profound than first appears. And far more ignored, it seems.

There are three branches of government, Congress (the legislative branch), the President (administrative branch) and the Supreme Court and such inferior courts as Congress may establish (the judicial branch). Only the Congress has the constitutional power to legislate. How then can an administrative agency, constitutionally under the President, adopt regulations that have the effect of law?

In theory, administrative regulations have only the power to clarify, interpret and fill in the gaps in legislation (an interpretative function of sorts), and then only where Congress has given that agency the power to adopt regulations. In practice, administrative agencies effective create law all the time.

It is not uncommon for lawyers to challenge agency rulemaking on "separation of powers" grounds. That means the lawyers are challenging the regulation going too far in enacting a law, thus encroaching on the power of Congress to make laws.

In theory, the judicial branch may only interpret laws enacted by Congress. The courts theoretically cannot make law. Of course, Congress enacts laws in English. In the English language, ambiguity abounds. Courts need to interpret. However, inevitably there are gaps. And the Constitution has huge gaps. The courts must decide cases, so decisions appearing to be judicial legislation are unsurprising.

Nevertheless, it seems the courts have occasionally (or more often) gone too far. If the Supreme Court goes too far, there is no one to correct it.

Still, the Constitution is quite clear. Only Congress has the power to enact laws.