The EU is expected to set out later the action it will take against Google over alleged anti-competitive behaviour.
Margrethe Vestager, the competition commissioner, could make a statement about her intentions on Wednesday.
Reports suggest she will announce that a “statement of objections” is being prepared.
Such action would mark an escalation in the Commission’s handling of complaints that Google favours its own products in search engine results.
Google accounts for more than a 90% share of EU-based web searches.
The company has yet to respond.
The European Commission has investigated the antitrust allegations – made by Microsoft, Tripadvisor, Streetmap and others – since 2010.
They object to the fact that the firm places reviews from Google+, directions from Google Maps, music and videos from YouTube, and adverts from its Adwords platform ahead of others’ links in relevant searches.
“At the core must be the fundamental principle that Google must not abuse its power in general online search to give preferential treatment to its own separate services,” Icomp, a lobbying group representing the complainants, said earlier this year..
“If Google takes the view that users are best served by search results that integrate additional services, Google must choose the services that benefits consumers most, even if the services are not its own.”
Last year, Google agreed to alter the way it displayed its search results, but the changes it suggested were deemed to be insufficient.
The previous competition commissioner, Joaquin Almunia, asked the company to come up with a new plan.
He left his post without resolving the matter, and was criticised by some politicians for not having taken a firmer stance.
Ms Vestager, his successor, may take a tougher line by issuing a “statement of objections”.
This involves sending a letter that sets out all the objections the commission can base its final decision on, and is a legal requirement, providing Google an opportunity to respond before action is taken.
Google could face huge fines and orders to reshape its business in Europe.
In recent years, the Commission has imposed antitrust penalties on other tech giants, ordering Intel to pay 1.1bn euros (£793m; $1.2bn) in 2009 and Microsoft 516m euros in 2013.
Thomas Vinje, spokesman for FairSearch Europe, said issuing a statement of objections would “represent a significant step towards ending Google’s anti-competitive practices, which have harmed innovation and consumer choice”.
“Google is a gatekeeper to different markets, and I think they will want to make an example of it,” said Paul Henty, a lawyer at Charles Russell Speechlys who has previously worked for the European Commission.
“But I can’t see that this will be a fast process given the complexity of the subject matter, what’s at stake and the likely level of the fine.”
The EU’s investigation is not the only one Google is facing.
Investigators at India’s Competition Commission delivered a report last week after carrying out a three-year probe into claims of unfair business practices.
Their counterparts in Russia, Brazil, Argentina, Taiwan and Canada have also opened investigations.
However, the US Federal Trade Commission dropped its own probe at the start of 2013 after Google made several non-binding commitments.