It my state and county it is legal to take fox any day of the year, all year, except Sunday. This may be a very good opportunity to really educate this man's son so I would not be showing a very angry attitude when talking to them. As much as this is very bad if it can be turned into a learning experience then maybe some good can come out of it. Also, as part of educating them you may want top explain that the taxi will turn them because he is required to by law or he could be liable for fines and jail also. Show how them how many ways that this is a bad thing to do.