Microsoft has complained to the European Union about Google which it says impedes internet search competition.
The US software company claims that Google's search engine engages in a "pattern of actions" which discriminates against competitors.
Microsoft's General Counsel Brad Smith said in a blog post that the internet search giant has a "broadening pattern of walling off access to content and data that competitors need to provide search results to consumers and to attract advertisers".
It is the first time Microsoft, itself the target of anticompetition action in the US and Europe, has filed a formal complaint with regulators over competition issues.
Its own search engine Bing has struggled to dent Google's 90 per cent market share of the European internet search advertising market.
Google is already under investigation by the European Commission after complaints from three small firms, including Ciao which is owned by Microsoft.
Google did not seek to counter Microsoft's claims publicly, but indicated it was not overly concerned by the complaint.
"We're not surprised that Microsoft has done this, since one of their subsidiaries was one of the original complainants," a Google spokesperson said.
"For our part, we continue to discuss the case with the European Commission and we're happy to explain to anyone how our business works."
Microsoft said it felt it was time to challenge Google on legal grounds directly, after publicly encouraging companies last year to question Google's practices.
"As troubling as the situation is in the United States, it is worse in Europe," said Smith.
"That is why our filing today focuses on a pattern of actions that Google has taken to entrench its dominance in the markets for online search and search advertising to the detriment of European consumers."
The suit alleges that Google hurts competition by:
- "walling off" content on its YouTube site, so other search engines can't display accurate results
- making it difficult for Microsoft's mobile phone software to show videos from YouTube
- blocking access to content owned by book publishers which Google has copied and stored
- not allowing advertisers to use their own data about customers garnered from Google on other sites, such as those owned by Microsoft
- blocking websites from using competing 'search boxes', and
- making it expensive for potential competitors to Google to advertise online.
"We readily appreciate that Google should continue to have the freedom to innovate," said Smith.
"But it shouldn't be permitted to pursue practices that restrict others from innovating and offering competitive alternatives.
"That's what it's doing now, and that's what we hope European officials will assess and ultimately decide to stop."