The developers of several adult-oriented visual novels say they’ve received letters from Valve informing them that their games won’t be published on Steam due to their characters appearing to be under age.

Steam pages for several adult-themed games have been pulled down in the last couple weeks, Kotaku reports. Those include Cross Love, Hello Goodbye, MaoMao Discovery Team, and Imolicious, all of which have characters who appear to be of high school age and younger. However, the developers all say their games have taken steps to make it clear that their characters are at least 18 years old.

Top Hat Studios, developers of Cross Love, shared the email they received from Steam on Twitter.

“While we can ship most titles on Steam, we found that this one does features themes of child exploitation,” it read. “Because of that, the app has been banned and cannot be reused.”

Top Hat went on to say they believe Cross Love is being targeted not because it has young-looking characters, but because it tells the story of a yaoi romance in which one partner is a cross-dressing male. Further, the studio says, it has taken pains to show in the story that both parties are at least 18 years old, going beyond the usual disclaimer card at the opening of the game.

Hello Goodbye’s publisher explained to Kotaku that the Steam version of the game was going to be censored so as to remove adult content.

Valve has been wrestling with how to handle sexual content on Steam for most of the year. Earlier in 2018, the company sent out letters to the publishers of numerous sex-themed visual novels, telling the developers they had two weeks to censor their games or be removed. After a short but intense protest, Valve relented and said it would not police content on Steam except in the cases of games that were “illegal, or straight up trolling.”

As Valve and developers have found out since then, that’s not as clear a line as it initially sounds. While developers argue that their explanations of characters being 18+ are sufficient to make whatever they’re depicting legal, Valve doesn’t appear to agree and has opted not to publish certain games.

And as Kotaku notes, that’s Valve’s prerogative, since it owns the storefront. For these developers, there are always other options – some have gone to itch.io, while others have opted for more hentai-centric sites like Nutaku and Fakku. But the loss of the revenue potential in Steam’s large user-base will make it tougher for them to turn a profit.