Does Google purposely degrade its search results to promote its own services? A new study says yes.

The study, co-written by Tim Wu, author of The Master Switch: The Rise and Fall of Information Empires, argues that Google knowingly serves up its own content in search results, even when it's not as good as competing sites, and consumers are being harmed by this anticompetitive behavior.

"By prominently displaying Google content in response to search queries, Google is able to leverage its dominance in search to gain customers for this content," according to the study, which was co-authored by Harvard's Michael Luca and the Yelp data science team. "This yields serious concern if the internal content is inferior to organic search results."

To investigate the issue, the researchers set up a randomized controlled trial in which they varied the search results users see—comparing Google's "current policy of favorable treatment of Google content" to results showing non-Google content. The researchers found that users prefer "organic" search results to those promoting Google's content.

In fact, users are 45 percent more likely to engage with content when "the results are organically determined," according to the study, which was presented at the Antitrust Enforcement Symposium in the U.K. over the weekend.

"This suggests that by leveraging dominance in search to promote its internal content, Google is reducing social welfare — leaving customers with lower quality results and worse matches," according to the study.

Google did not immediately respond to a request for comment about the report.

It should be noted, however, that Yelp, which reportedly paid Wu for his research, has long taken issue with Google's search practices.

In 2011, the review site faced off against Google on Capitol Hill and accused it of threatening to pull Yelp content from search entirely if Yelp didn't allow Google to use Yelp content on its Place pages.

But Google has been under investigation around the world for similar practices. In 2013, the U.S. FTC found that Google did not unfairly manipulate its search results to highlight its own products and demote competing firms. Across the pond, however, the EU in April formally accused Google of abusing its power when it comes to search, and opened a separate probe into the company's Android mobile operating system.