In League, If he does it during warm-up, just give him a heads ups that he's doing it and its against the rules. AND, you'll call it. (Fair Warning)
If he continues once the match starts, I'd give him "One" warning, then I'd call it everytime.
We had one in our league that was known for foot faulting. When it came my turn to play him, I followed the above.
Even poached in to the service line just to watch him do it. That rattled him ALOT!
Eventually, he became so frustrated that he walked off and forfitted all the games.
One of the more seasoned league players Thanked Me after the match. Said he wished someone would have done that years ago....