Google has been ordered to pay a record fine of £2.1bn (€2.42bn) for abusing its dominance as a search engine to boost its shopping comparison service.
The European competition watchdog said the company had breached anti-trust rules.
It said Google's search engine had systematically given prominence to its own comparison shopping service over others, so that it was displayed at or near the top of search results.
The company has been ordered to end the conduct at the centre of the European Commission probe or face penalty payments of up to 5% of the average daily turnover of parent company Alphabet.
Google said it "respectfully" disagreed with the ruling and would review the decision in detail as it considers an appeal. Its shares were 1% lower in early US deals.
Commissioner Margrethe Vestager, in charge of competition policy, said Google's innovative products and services had been "a good thing" but its strategy for attracting customers to its online shopping service was not just about being better than rivals.
"Instead, Google abused its market dominance as a search engine by promoting its own comparison shopping service in its search results, and demoting those of competitors," she said.
"What Google has done is illegal under EU anti-trust rules.
"It denied other companies the chance to compete on the merits and to innovate.
"And most importantly, it denied European consumers a genuine choice of services and the full benefits of innovation."