This is exactly why companies have a strict policy against employees revealing their salaries for each other. Let's say, for example, you have Jane and John. They both do the same work and they share the assumption that each make the same salary as they have both been at the company for the same amount of time.
John learns that Jane makes more money than he does and is furious. It doesn't matter that his lifestyle does not depend one bit on what Jane makes -- the chances are good John will be furious because it is not fair (i.e. not equitable) that Jane makes more money than he does.