Income mobility charts for girls, Asian-Americans and other groups. Or make your own. It's the latest sign that this has become the policy of choice for shrinking the gender pay gap . Several states, cities and companies have recently banned asking about salary history. They include Massachusetts, California, New York City, Philadelphia and Chicago, as well as Amazon, Google and Starbucks. Women continue to earn less than men, for a variety of reasons . Discrimination is one, research shows.