I first discovered this because I follow Soraya on both twitter and facebook, and I read almost everything she writes. She's my favorite current writer and activist. She tweeted a link to the open letter to facebook that she co-authored with Laura and Jaclyn.
(I was also familiar with Laura because she created Everyday Sexism, a blog that chronicles the sort of commonplace sexism women (and sometimes men) face, via user submission. Jaclyn is new to me, but she founded Women, Action, and the Media).
According to facebook's policies, "You will not post content that: is hate speech, threatening, or pornographic; incites violence; or contains nudity or graphic or gratuitous violence."
The problem is how this is enforced. Photos of women post-mastectomy or of women breastfeeding are removed for "violating" policy. But photos of women being beaten or raped don't violate policy... Accounts who call out sexism on facebook are banned or deleted. Groups called, "Dumping your girlfriend via head kick" stay up.
We are calling on facebook to change its policies, and until they do so, we're calling on companies to pull their ads from facebook. Some companies have already done so!
You can help by commenting on company's facebook pages, tweeting at them, and emailing them. Personally, I have been in touch with Shabby Apple, who has promised to look into it. I hope they do the right thing and pull their advertising.
I am only one voice. But if we all work together, we CAN make a difference.