The European Commission, the EU antitrust regulator in the 27-country European Union, said it had opened two investigations into Motorola Mobility based on complaints by Microsoft and Apple.
The EU executive will investigate whether Motorola failed to honour "irrevocable commitments" it made to standard-setting organisations, which produce international standards for information and communication technologies.
It will also consider whether Motorola offered unfair licensing conditions for its standard-essential patents. It can fine companies up to 10% of their global turnover if found guilty of breaching EU rules.
Microsoft asked EU antitrust regulators in February to intervene in its patent dispute with Motorola.
Commission may also investigate smartphone maker Samsung
Google had pledged to license Motorola patents on fair and reasonable terms just before EU regulators cleared its bid to buy Motorola.
EU regulators are also investigating whether Samsung Electronics Co Ltd has infringed EU antitrust rules in its patent disputes with Apple in courts across Europe.
EU Competition Commissioner Joaquín Almunia said last month that companies holding these "standard essential" patents had considerable market power, which could be used to harm competition and that this was unacceptable.
Almunia said last September that Google's planned purchase of Motorola Mobility Holdings Inc. will not influence an ongoing antitrust probe into the Internet search engine, which he is currently considering.