BRUSSELS (AP) – Microsoft today lodged a formal complaint with the European Union's competition regulator against Google's Motorola Mobility, saying the company's aggressive enforcement of patent rights against rivals breaks competition rules.

The complaint follows a similar step by Apple against Motorola Mobility last week. The Libertyville, Ill.-based company is in the process of being taken over by Google for $12.5 billion, the biggest acquisition in the Californian company's history.

Apple Inc. and Microsoft Corp. have been hit by legal cases in Europe and the United States, with Motorola Mobility claiming that the companies' products are using key patents it owns without permission.