The 19 companies, which include US online travel site Expedia, US consumer reviews website Yelp, online mapping service Hot-map and British price comparison site Foundem, helped triggered the European Commission's case against Google nearly five years ago.
That culminated in the EU competition authority levying charges against the world's most popular Internet search engine two months ago, raising the possibility of a fine of as much as $6.6 billion (roughly Rs. 42,352 crores), 10 percent of its global turnover.
The Commission said Google had abused its market power and cheated consumers and competitors by distorting web search results to favour its own shopping service. The case could radically change the way the company operates in Europe.
Google has until July 7 to respond to the accusations. This can be extended on request. It can also seek a closed-door hearing to argue its case before a broad audience of antitrust officials and the critics.
The complainants were told on Monday to sign confidentiality waivers not to disclose the so-called statement of objections to journalists or public affairs consultants before they could get a copy of the redacted document, according to a Commission letter seen by Reuters.
The critics were told to restrict the charge sheet to their lawyers and economists.
Commission spokesman Ricardo Cardoso declined to comment. Google spokesman Al Verney was not immediately available to comment.
European Competition Commissioner Margrethe Vestager has marked her tenure with a series of landmark cases since taking up the job in November, notably charges against Russian gas giant Gazprom and investigations into Amazon, Apple and Starbucks.
© Thomson Reuters 2015