Senator Elizabeth Warren on Wednesday called for an investigation of Google’s alleged manipulation of online advertising. 

In a letter to the Commodity Futures Trading Commission (CFTC), Warren points to Project Bernanke, which The Wall Street Journal detailed in April after the media company found a description in court documents filed in a Texas antitrust lawsuit that alleges the project gave Google an unfair advantage.

Google’s Project Bernanke reportedly boosted its own ad-buying platform over competitors, and this was not disclosed to publishers that sold ads through Google’s ad-buying systems. It generated hundreds of millions of dollars in revenue for the company annually, the documents show.

The court document filed by Warren on Monday explains that Google gathered bid data through its ad exchange, AdX, from other market participants and then used that data to give its own ad-buying systems, DV360 and Google Ads. 

“Because Google was able to learn from rival ad buyers’ previous bidding data, its ad- buying tools gained a competitive advantage that ultimately boosted their win rates,” Warren wrote. “Google’s ad-buying products thus became more attractive than those offered by rivals, killing off other competing ad buyers that could not deliver advertisers the same win rates as Google.”