Never heard of anything like this before. Sounds like an over agressive tie dealer look to make a large profit margin off selling cheap ST tires.
Check the BC regulations
HERECan't find anything in them that makes any such prohibition.
What about large 5vers that come from the factory with LT's, what would BC do?
Perhaps someone from BC could provide further info and context, but research does not suggested that LT's are prohibited.