Microsoft looks to be facing yet another antitrust probe after it emerged on Tuesday that Spain’s competition watchdog, the National Competition Commission, has opened a case against Microsoft’s local and Irish units over allegations that the company had blocked the sale of Microsoft software licenses by third parties.

The National Competition Commission made the announcement in a press release, noting that the investigation was launched after collecting information that could indicate a potential violation of competition regulations.

Microsoft is no stranger to antitrust investigations, with the Redmond-based company having already judged to be charging competitors too much for interoperability information for its servers. The company was fined €497m in 2004 but the European Commission added another €899m to the fine in 2008 for failing to comply with the original anti-trust ruling.

The company waited until May 2011 before launching an appeal against the €899m antitrust fine it received from the European Commission in 2008. The company described the fine in court as “Excessive” and “Most undeserved”.

According to reports, the Spanish investigation and subsequent ruling will need to be completed within the next 18 months. We have contacted Microsoft for comment.