If they’re trying to protect themselves from code injection by rejecting certain user input like that, then they don’t actually know how to protect themselves from code injection correctly and there may be serious vulnerabilities that they’ve missed.

(I think it’s likely that, as others have said, they’re using off-the-shelf software that does properly sanitize user input, and that this is just the unnecessary result of management making ridiculous demands. Even then, it’s evidence of an organization that doesn’t have the right approach to security.)