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.
In its decision on Friday, the Commission accused Google of self-preferencing its own technology above others.
As part of its findings, it said Google had intentionally boosted its own advertising exchange, AdX, over competing exchanges where ads are bought and sold in real-time.
The regulator has ordered the company to bring such practices to an end, as well as pay the nearly €3bn penalty.
Third Time Rules Broken
The Commission's fine is one of the largest fines it has handed down to tech companies accused of breaching its competition rules to date.
In line with our usual practice, we increased Google's fine since this is the third time Google breaks the rules of the game, said Teresa Ribera, executive vice president of the Commission.
Ms Ribera also warned the tech giant it had 60 days to detail how it would change its practices, or else the Commission would look to impose its own solution.
