The Chicago Tribune filed a lawsuit against AI search engine Perplexity on Thursday alleging copyright infringement. The suit, seen by TechCrunch, was filed in a federal court in New York.

The Tribune alleges that its lawyers contacted Perplexity in mid-October asking if the AI search engine was using its content, according to the complaint. Perplexity’s lawyers replied it did not train models with the Tribune’s work, but that it “may receive non-verbatim factual summaries,” the lawsuit claims.

The Tribune’s lawyers, however, argue that Perplexity is delivering Tribune content verbatim.

Interestingly, the newspaper’s lawyers are also calling out Perplexity’s Retrieval Augmented Generation (RAG) as a culprit. RAG is a method used to limit hallucinations by having the model only use an accurate or verified data source. The Tribune argues that Perplexity is using the newspaper’s content in its RAG systems, scraped without permission. Plus, it alleges the Perplexity’s Comet browser is bypassing the paper’s paywall to deliver detailed summaries of those articles.

The Tribune is one of 17 news publications from MediaNews Group and Tribune Publishing that sued OpenAI and Microsoft over model training material in April. That suit is ongoing. Another nine from these publishers sued the model maker and its cloud provider in November, too.

While creators have filed many lawsuits against model makers over using their work for model training, we’ll have to see if the courts weigh in about the legal liabilities of RAG as well.

Perplexity did not immediately respond to the Chicago Tribune’s story about its own lawsuit, nor to TechCrunch’s request for comment. Perplexity is facing other such suits. Reddit filed one in October. Dow Jones is also suing. Last month, while Amazon didn’t sue, it did threaten to by sending a cease and desist letter over AI browser shopping.