This kind of law can only come from the Ezra Klein school of thought on the constitution. After all what in the world could the first amendment mean when it says "congress shall make no law... abridging the freedom of speech". Must mean that you can outlaw certain kinds of speech, right?
Of course this will be an interesting case to follow and has good potential to make blood shoot out of my eyes. And, of course, the concern the government is trying to address here could be done in a much better way by the private sector itself as Ed Morrissey points out.
The imposition of licensing is usually prefaced on the need to keep consumers from being defrauded, but mainly they serve as barriers to entry for smaller operators in any field while protecting the larger players. The tour-guide industry could police itself through voluntary associations that require particular types of expertise, training, and consumer protection rather than have the government impose that through unnecessary — but revenue-producing — licensing regimes.