I happened to be channel surfing a couple of years ago and they were together on a show called "Nash Bridges" - Don Johnson was with his partner from Miami Vice on the same show too.
Sounds like a classic Nash Bridges, I hope I get to see it on a re-run sometime. Cheech Marin was the best part of that show I always thought.
Cheech was Don Johnson's partner on the series and Tommy Chong was playing a mob acountant, or some such, that was cooperating in a bust. Cheech and Chong went to a "Medical Marijuana Club" smoking room to bust one of the suspects, who was stoned out of his gourd. This resulted in one of my favorite lines on TV ever.
Cheech flashed his badge at the suspect and said something to the effect:
"step away from the bong and keep your hands where I can see them."
And yes, it was a classic episode.