Amazon, Apple, Facebook and Alphabet unit Google may have to change their business practices in Europe or face hefty fines between 6-10% under new draft EU rules to be announced on Tuesday.
The rules are the most serious attempt by the 27-country bloc to rein in the power of the US tech giants which control troves of data and online platforms on which thousands of companies and millions of Europeans rely on.
They also mark the European Commission's frustration with its antitrust cases against the tech giants, notably Google, which critics say did not address the problem.
Regulatory scrutiny has been growing worldwide of tech giants and their power.
European Competition Commissioner Margrethe Vestager and EU Internal Market Commissioner Thierry Breton will present the rules, a bid not just to rein in tech giants but also to prevent the emergence of anti-competitive dominant companies.
One set of rules called the Digital Markets Act calls for fines up to 10% of annual turnover for online gatekeepers found breaching the new rules, a person familiar with the matter told Reuters.
It also sets out a list of dos and don'ts for gatekeepers, which will be classified according to criteria such as number of users, revenues and the number of markets in which they are active, other sources said.
The second set of rules known as the Digital Services Act also targets very large online platforms as those with more than 45 million users.
They will be required to do more to tackle illegal content on their platforms, misuse of their platforms that infringe fundamental rights and intentional manipulation of platforms to influence elections and public health, among others.
The companies will also have to show details of political advertising on their platforms and the parameters used by their algorithms to suggest and rank information.
The draft rules need to reconcile with the demands of EU countries and EU lawmakers, some of which have pushed for tougher laws while others are concerned about regulatory over-reach and the impact on innovation.
Tech companies, which have called for proportionate and balanced laws, are expected to take advantage of this split to lobby for weaker rules, with the final draft expected in the coming months or even years.