The sex pay has been around forever and for obvious reasons men do not want it to go. In addition to keeping the money for the selves they use the sex pay gap as a mechanism for female oppression.
So, if a law was passed that made men pay a higher rate of tax than women then several benefits would follow. This would immediately eradicate the sex pay gap. Men would have less power over women. Also the extra money raised could be spent on women's only charities and could be seen as reparations that are long overdue.