The complex mess of patent-related battles in the mobile industry has taken another twist. It’s emerged that Apple has filed a formal antitrust complaint against Motorola Mobility to the European Commission.

Apple’s complaint emerged in Motorola Mobility’s latest annual report, filed yesterday. As FOSS Patents notes, the document reveals that the company has only just been informed of the complaint:

“On February 17, 2012, the Company received a letter from the European Commission, Competition Directorate-General, (the ‘Commission’) notifying it that the Commission has received a complaint against Motorola Mobility, Inc. (‘MMI’) by Apple, Inc. (‘Apple’) regarding the enforcement of MMI’s standards-essential patents against Apple allegedly in breach of MMI’s FRAND commitments. Apple’s complaint seeks the Commission’s intervention with respect to standards-essential patents.”

The complaint relates to Motorola Mobility’s handling of patents that it holds which are classified as requiring licensing to others on ‘fair, reasonable, and non-discriminatory‘ (FRAND) terms. This is designed to ensure that companies do not use patents to monopolise a sector by offering unreasonable licensing terms.

Apple believes Motorola is in breach of this commitment, something also evident in its recently initiated lawsuit in the US.

A Motorola Mobility spokesperson has told Bloomberg Businessweek that the company “has a long-standing practice of licensing our patents on fair, reasonable and non-discriminatory terms and we offered those to Apple,” adding that the two companies have been in licensing talks since 2007.

Earlier this week, the European Commission approved Google’s acquisition of Motorola Mobility. However, it expressed concerns over Motorola’s handling of patent licensing. FOSS Patents noted earlier in the week that such concerns could not be dealt with as part of a mergers and acquisitions procedure.

With Samsung already under investigation by the European Commission for its approach to licensing patents, it seems likely that Apple’s complaint will be taken forward into a formal probe.

Meanwhile, as noted by Slashgear, Motorola also notes that it sees one potential threat this year being Nokia entering the tablet market. Back in December 2011, Nokia CEO Stephen Elop said that Nokia “does not have an exact plan” with regard to tablets, but that it was “studying the markets carefully.” If a Nokia tablet emerged that was anything near as nice as these fan-made renders, Motorola would definitely have cause for concern.