There is the 16th amendment. However, I do not know of any law congress passed that says we must pay income tax. There is tax code from the IR$, but that seems more like a mandate which s not a law. I would really like to understand this better. It is also important to note that SCOTUS struck down Chevron Doctrine last year. This means the courts do not refer these things to agencies anymore. The courts can now rule based on law, not the opinion of an agency. If no law, no taxes....