Of course it's legal. Basically bus drivers are told not to hold up an entire bus route just to call police to come and arrest someone who won't pay a fare. Even with that in place I have sat on a bus in peak hour traffic while some jackass bus driver yelled at someone who had accidentally got on the wrong door and made them squeeze through a whole crowded bus to swipe their stupid orca card. As if that was worth holding up everyone on the bus, plus the bus behind that couldn't get to the stop, etc.

Thanks for clarifying.