My mother used to work for an abused women's shelter which paid their male employees $7k less than their female employees across the board. As you can imagine, they had a bit of a feminist bent and thought this was fair. The male employees obviously thought otherwise. This is the only example I know of of people systemically being paid different rates for the same work based strictly on gender.
The cited pay gap is actually for ALL women compared to ALL men, and not for men and women working the same job with the same level of experience, etc. Feminists distort these facts for propaganda. It's been illegal to pay women less for the same work since 1963 in the US. It's also been illegal in most, if not all Western countries at varying dates, but most go back at least 40-50 years.