For Alexandra Tweten, unsolicited dick pics just seem to be a part of modern life. As a single woman in Los Angeles and an active online dater, she has seen more than her share of photos of men’s genitalia—but never because she asked for them.

She’s far from alone. After talking with friends and other women online, Tweten realized that this obscene ritual is surprisingly common. And it’s not just limited to dating apps: A shocking number of surprise phalluses find their way into women’s inboxes on Facebook. And they’re really, really tired of it.

“We shouldn’t have to deal with this,” Tweten says. “It’s fucked up.”

So Today, Tweten is launching a Change.org petition calling on Facebook to more explicitly ban the act of sending unsolicited sexual imagery. This behavior, she says, is analogous to a man flashing his genitals to a woman on the street. But although laws forbid such conduct in public, there are few protections against it online. This is true in just about any digital space, but the campaign is initially focusing its critique on Facebook as the world’s largest social network. In the future, Tweten plans to apply pressure to other online communities and, eventually, hopes to see a legislative solution to the problem.

Alexandra Tweten

“I have personally been a recipient of unsolicited dick pics on Facebook, and it made me feel both degraded and fearful for my personal safety,” Tweten explains. “One man has made several different Facebook accounts to send me pictures of his penis. I block him, but he makes another.”

Although Facebook has rules in its community guidelines barring people from posting nudity and sexual images publicly, those rules don’t directly address images that are sent privately. Under the guidelines’ section on bullying and harassment, Facebook does forbid “repeatedly targeting other people with unwanted friend requests or messages,” and while it’s fair to interpret “unwanted messages” to include lewd photos, Tweten says this clause isn’t specific enough. And even if it were, the word “repeatedly” would seem to permit the first dick pic, but forbid subsequent images. At no point in Facebook’s guidelines is privately sent, unwanted sexual imagery defined as a form of harassment. This is the sort of language—along with the appropriate penalties—that Tweten would like to see added to Facebook’s rules of conduct.

Facebook’s guidelines–which vow to “remove photographs of people displaying genitals”–presumably apply to its Messenger app, but it’s not clear if Facebook actively polices private messages or deals with obscene, private imagery as it’s reported. We reached out to Facebook for clarity and will update this story with any new details.