According to an article in HR Review (https://goo.gl/kMe6Hi) Icelandic women are protesting at the 14% gender pay gap in Iceland by leaving work 14% early. How effective it will be only time will tell.
Of course, in the UK the gender pay gap is a bit less at 9.4% for full time employees, so a similar protest (even if it could be lawfully carried out) would have rather less impact.
Obviously, another way to approach the issue might be to find a way to start a dialogue with your employer or (dare we suggest?) seek to engage in workplace mediation. There is a time and a place for symbolic protest, but there should always be time to talk too.