The European Commission has today sent out information requests to the companies whose initial complaints led to a three-year antitrust investigation into Google's search practices.

The EC said on Monday that it has requested opinions from the complainants on measures put forward by Google to ease Europe's concerns over its dominance of the search market in Europe.

Google published its proposed remedies earlier this year, which included better labelling of search results to show when its promoting its own services, an opt-out to allow companies to stop their content from appearing in Google services such as local search, and letting advertisers move their campaigns away from Google more easily.

However, Joaquín Almunia, the EC's competition commissioner, demanded more from Google, saying the proposals were not enough to allay the EC's concerns — a sentiment echoed by some of Google's rivals . Google subsequently offered up a revised set of concessions , which the EC is now seeking opinions on.

"In the context of the ongoing antitrust investigation, the Commission is seeking feedback from complainants and other relevant market participants on the improved commitments proposals by Google, as announced by vice president Almunia on 1 October ," a spokesman for Alumnia said in a statement.

To that end, the Commission is sending today information requests... information is sought, in particular, from complainants in the ongoing proceedings and from all those who responded to the initial market test of Google's proposals which the Commission launched in April.

The EC opened the antitrust probe into Google in 2010 after rival search companies alleged they had received unfavourable treatment of their services in Google's unpaid and sponsored search results. Among the companies that have filed complaints about Google's search practices are Microsoft , UK search engine Foundem and travel site Expedia .

ZDNet has asked Google for comment and will update the story if any is received.