Is it true there's no law requiring income tax?

I was listening to an NPR interview with a congressional aid. In this interview they were discussing a law that had been recently passed (not a tax law). The aid said now that they had passed it it was up to the courts to decide what the law meant.

With that attitude in our representatives, I bet you could get a law passed typeset in Zapf Dingbats, and no one would notice until it was challenged in court.