Dating app Tinder is going after 3nder, a small U.K.-based app for those who believe the more, the merrier.
Tinder, which is part of dating service giant IAC, has filed a lawsuit against 3nder in an English court for infringing its trademark, according to multiple media reports. Tinder is reportedly accusing 3nder, an app that lets couples meet potential threesome mates, of choosing a name that sounds very similar to its own, and wants the startup to shut down and remove all references to itself from the Internet to avoid confusion with Tinder.
In a letter sent to 3nder in December, lawyers for Tinder cited an interview with 3nder’s founder, Dimo Trifonov, published in the New York Post in which he mentioned one possible pronunciation of his app’s name.
“Phonetically, the infringing mark is closely similar to the Tinder mark, as the obvious pronunciation of ‘3nder’ is ‘Thrinder’, which rhymes with Tinder,” reads the letter, according to The Guardian, which has obtained a copy of it.
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The startup countered that “the journalist said 3nder could be pronounced to rhyme with Tinder, but in no way implies that is the official pronunciation,” according to a statement sent to the New York Post on Monday, which also pointed to a separate story in which a different pronunciation is offered. It also argued that other dating apps, like Grindr, use a similar name ending and debuted before Tinder, showing that the company doesn’t have a monopoly on the name.
On Monday, 3nder fired back at Tinder with the launch of a social media campaign asking its users and fans to send pictures of their socks with the hashtag #TinderSuckMySocks to Tinder because Trifonov has been so busy fighting this threat that he’s forgotten to do his laundry, he wrote in a blog post.
The spat with Tinder threatens to bankrupt 3nder, which raised a small $500,000 seed round last year from an unnamed investor, and its users’ $13 monthly membership fees. In his blog post, Trifonov said that in the past year, 3nder’s revenue has grown nearly 10-fold and 30% growth in new members.
“With our sudden market growth, makes sense to come after us now, right? Our vision to break down silly taboos in modern society is happening. And Tinder doesn’t really know what to do with open minds. So they want us out of their way,” he wrote.
Last fall, Tinder was the subject of a lengthy report in Vanity Fair exploring the fast and loose “hookup culture” among young adults in major cities like New York. Tinder, and other apps like it, the story alleged, has become a common tool for young adults looking for short physical encounters with others. Tinder aggressively denied that many of its users were turning to the app for that purpose.
The Bulgarian-born Trifonov released 3nder in mid-2014 as a response to his long-time girlfriend’s confession she was attracted to a French woman.
Fortune has contacted 3nder and will update if we hear more. Tinder declined to comment.