What you need to know:
- Google called the claims "meritless", saying that the way publishers such as Associated Newspapers use its ad technology makes no difference to its placing in searches.
The British owner of the MailOnline website on Wednesday filed a legal complaint in the United States against Google, accusing it of downgrading its stories in searches.
London-based Associated Newspapers Ltd filed a legal suit at a New York court, accusing the tech giant of reducing its search traffic and asking for damages and legal costs.
The MailOnline is the fifth most popular US news website, the media group says. Stablemates include the Daily Mail tabloid and the Mail on Sunday weekly.
Google called the claims "meritless", saying that the way publishers such as Associated Newspapers use its ad technology makes no difference to its placing in searches.
Google says it makes most of its money from showing ads alongside relevant search results.
Associated Newspapers' complaint centres on the way that the highest bidder is instantly selected for advertising space every time someone accesses a page.
Google's dominant DoubleClick Ad Exchange (AdX) system allows advertisers to bid to put ads on web pages.
MailOnline has been using "client-side header bidding", where publishers can attract outside bids, increasing competition for advertising space.
Google "punished" the website "because Daily Mail's pages were less profitable to Google than other websites," the legal complaint claims.
"For years, Google substantially has eroded Daily Mail's search traffic," it claims, accusing Google of using its "monopoly search engine to entrench its ad-tech dominance".
It said the problem "persists to this day", adding that since the beginning of the year, Daily Mail's US search traffic has fallen more than 50 percent.
Google has faced increasing scrutiny along with other tech behemoths that dominate key economic sectors.
Anti-trust actions against Google have been filed in the US and elsewhere.