Tech giant Google has lodged an appeal against the 2.4bn euro fine (£2bn / $2.8bn) it was ordered to pay by the European Commission in June.
The regulator had ruled that positioning its own shopping comparison service at the top of Google search results was an abuse of power.
The fine was the largest penalty ever issued by the regulator, which also said the firm could face more fines if it continued its practices.
Google said it had no further comment.
At the time that the fine was imposed, Margrethe Vestager, the European Union's Competition Commissioner said that Google's activity was "illegal under EU antitrust rules".
A spokesman then said that Google "respectfully disagreed" with the ruling.
Google was also given 90 days to end the "anti competitive" practices or face a further fine amounting to 5% of the average daily global earning of its parent company Alphabet.
The deadline for making the changes is 28 September.
Analysis: Rory Cellan-Jones.
It is hardly a surprise that Google is appealing against the record fine handed down to it by the EU.
When the Competition Commissioner Margarethe Vestager ruled against the search giant, the move was seen as just the first shot in a wider campaign.
The Commission is looking at other areas where it suspects Google may have abused its monopoly power, notably its Android mobile operating system - so the American firm did not want to lie down and accept its fate.
This of course means that there will be plenty of work for lawyers and lobbyists for years to come.
Last week the Commission had a setback when the European Court of Justice ordered a review of a fine it imposed on the chip giant Intel. That dates back to 2009 - so don't expect Google's case to be done and dusted in the near future.