Google has been fined €2.95bn (£2.5bn) by the EU for allegedly abusing its power in the ad tech sector - the technology which determines which adverts should be placed online and where.
The European Commission said on Friday the tech giant had breached competition laws by favouring its own products for displaying online ads, to the detriment of rivals.
It comes amid increased scrutiny by regulators worldwide over the tech giant's empire in online search and advertising.
Google told the BBC the Commission's decision was wrong and it would appeal.
It imposes an unjustified fine and requires changes that will hurt thousands of European businesses by making it harder for them to make money, said Lee-Anne Mulholland, global head of regulatory affairs at Google.
US President Donald Trump also attacked the decision, saying in a post on social media it was very unfair and threatening to launch an investigation over European tech practices that could lead to tariffs.
In the Commission's decision on Friday, the Commission accused Google of self-preferencing its own technology above others.
The regulator has ordered the company to bring such practices to an end, as well as pay the nearly €3bn penalty.
This fine is the third imposed on Google for breaching competition laws, highlighting ongoing tensions between the EU and major US tech firms.
