What is "unwanted" sexual advances? Is it a colleague asking out for a drink, ignoring that the woman was already seeing someone or not interested in dating? It is "unwanted", but the colleague may just have been taking a shot. It is said that work is the main environment where people find their partner.

Now, if "unwanted" means "He asked, I declined and he kept asking me out every day after that" then yes it is a problem.