i say its totally unethical. the only thing i would say is find a way to tell them to stop or just go to your boss.
i have two related stories:
my mom: she worked with this woman who did the same thing, only then sent emails, mailing letters, and all through the company. she didnt do anything it just got worse.
my step dad: he worked with a group of people that did the same thing. he is a devoted Atheist. he rudely snapped back and was agressive. he ended gettting in trouble instead.
so go with the in between and tell your superiors. i know it sucks, because making a big deal out it is trouble, but it does help in the end.