The concept of tenure is definitely somewhat controversial, but it is incredibly difficult and rare to fire tenured professors. I doubt you could cite many if any examples of professors losing tenure because they're not publishing. (Although sure professors who don't publish probably won't receive tenure in the first place)
There are all manner of things a department can do to make a tenured, non-productive faculty member's life harder. The sudden loss of lab space is a particularly common one.
Also, keep in mind that a good many tenured professors are still in "soft money" positions, and have to bring in grant support for parts of their salary.
