In an article that appeared on BusinessInsider, Justice Alito declared that Congress cannot regulate the Supreme Court because “No provision in the Constitution gives them the authority to regulate the Supreme Court.”
As noted in that article, Ted Lieu responded quickly by pointing out at Congress can regulate the jurisdiction of the court and can, of course, impeach Justices.
But, more importantly, if he really wants to go by what is or is not in the Constitution, perhaps he should declare some of his own actions on the Court invalid because the most powerful tool of the Court — declaring laws unconstitutional — like it did to portions of the Voting Rights Act because Republicans in Congress are too cowardly to do it themselves — is also not in the Constitution. That rights was initially declared by the Supreme Court by Justice John Marshall in the famous case Marbury v. Madison. But nowhere does the Constitution say the Supreme Court can do so. So, if he wants to be a literalist, he cannot do what he seems to love doing most.
Of course, there is also nothing in the Constitution saying we cannot add justices or even that we are obligated to pay them for sitting on the Supreme Court. Of course, for Thomas and Roberts, that does not seem to be a problem because they generate lots of side benefits.