It is - most definitely...that would be a rule 2 violation. The problem is, though, the onus would be on you to prove that the other guy wasn't an idiot.

I was doing tactics/trimming on a boat with a talented, but somewhat inexperienced owner/helm, not too long ago where we had a finishing issue. We were windward sailing upwind to the starboard end of the finish line with a boat, pretty even and maybe slightly ahead, close and overlapped to leeward. Neither one of us were laying the starboard end of the finish line and both of us had to tack back to port starboard in order to finish. The lawyer helming the other boat, an experienced sailor who had a fairly unethical reputation, started screaming for room to tack while blurting something about overlap and zone, etc. I instructed our boat to hold course and tack on my call. My skipper flinched and tacked - we probably gave up that finish position at that moment but our crew wasn't ready for the tack and we got smoked to the line. The subsequent sheepish grin from the skipper of that other boat really got under my skin. I knew he knew that I knew he knew.