Ridiculous. I can only think of 2 scenarios which would have led to this. One, there was a conflict between some employees and they are want to avoid further conflicts. But there are already laws against discrimination and workplace bullying. Banning the topic outright is lazy. Or two, someone in management has strong opinions and can’t handle hearing an opposing view. Either way, management are being toddlers.
Also I’m no lawyer, but would this even be legally enforceable? Can an employer really ban topics of conversation at work?