Alphabet unit Google, Microsoft, and other tech giants will have to be more transparent in how they rank online search results, under European Commission guidelines out on Monday.
The guidelines, which take immediate effect, will be followed up next week by the publication of draft rules that could eventually impose further restrictions on the tech sector.
Smaller rivals and some companies have long complained about arbitrary and opaque practices tech giants employ that affect how their products and services are ranked in search results, especially when that means they are placed far below the bigger companies.
Google's online search practices have landed it total fines of more than 8 billion euros ($9.71 billion) over the period 2017-19 from EU antitrust regulators who found it had unfairly pushed its own products to the disadvantage of competitors.
The Commission said the guidelines require online platforms to identify the algorithmic parameters that determine ranking and to share them with companies.
"These guidelines set the standard for algorithmic ranking transparency and will increase fairness in the online platform economy, which drives innovation and welfare for millions of Europeans," European Competition Commissioner Margrethe Vestager said in a statement.
Vestager will on Dec. 15 present draft rules to rein in tech giants, setting out a list of dos and don'ts and increasing their responsibility to take down illegal and harmful content from their platforms, with fines and other sanctions to encourage compliance.
Neither Microsoft nor Google responded immediately to requests for comment.
($1 = 0.8243 euros)
(Reporting by Foo Yun Chee; editing by Barbara Lewis)