Google is squaring off against regulators from the European Commissions today in the EU Court of Justice in Luxembourg.

Google accused European Union antitrust watchdogs of blundering their way through a probe that culminated in a record €4.3 billion ($4.5 billion) fine for allegedly abusing the market power of its Android mobile-phone ecosystem.

The company is making its case at the European Court of Justice, the bloc’s highest court, on Tuesday after the regulator ruled that Google had unfairly used its dominance to make sure traffic on Android devices went to its search engine.