At my last office, most of the employees had their chairs locked in the upright position... but (before our chairs were replaced) all of the computer support staff left theirs unlocked. It was hilarious to see my boss sit down in one of them... because none of us would ever remember to lock them again... he would sit down, lean back, and panic when the chair started to recline. Net result? Our chairs were replaced with the most uncomfortable office chairs ever... and they didn't tilt. Net result to
that? All of the backs on the chairs became damaged fairly quickly, because we all leaned against them, and they were very flimsy.
I have seen many people tilting/reclining in their office chairs, though. I've never heard of a rule against it... I'm sure there is in some insane company somewhere, but I've never heard of it.