Chairman Gudni Bergsson resigned already on Monday evening - now the rest of the board follows.
The background is that a 25-year-old woman accused an Icelandic national team player of harassing her and another woman at a nightclub in Reykjavik four years ago.
The women reported the incident to the police and claim that the union was aware of the accusations.
So much so that a lawyer connected to KSÍ contacted her and offered her to sign a confidentiality agreement which also included financial compensation.
She refused to sign, but says that she instead made amends with the player who paid damages and apologized to her personally.
KSÍ issued an apology on Monday, writing, among other things, that they "let down" the women.