Google has filed a complaint with European regulators alleging that Microsoft has violated competition laws by waging a proxy patent war against Android. Google hasn't made the complaint available to the press, but a statement from the search giant alleged that "Nokia and Microsoft are colluding to raise the costs of mobile devices for consumers, creating patent trolls that sidestep promises both companies have made."

"They should be held accountable, and we hope our complaint spurs others to look into these practices," the statement said.

While Google itself has not been the target of many Android-related patent lawsuits (and recently prevailed in its fight with Oracle), the company alleges that the threat of lawsuits against companies that manufacture Android handsets are creating an unfair advantage for Microsoft's own Windows Phone platform.

A Google spokesman told Bloomberg that the complaint focuses on the transfer of 2000 patents to a litigious firm called Mosaid Technologies. According to Google, Microsoft has publicly pledged not to assert those patents against competitors, but is now attempting to get around that promise by passing the patents to a third party who is not bound by the same promise. Google says Microsoft and Nokia are entitled to a share of Mosaid's licensing revenues.

The complaint is a "desperate tactic," according to Microsoft. "Google is complaining about patents when it won’t respond to growing concerns by regulators, elected officials and judges about its abuse of standard-essential patents, and it is complaining about antitrust in the smartphone industry when it controls more than 95% of mobile search and advertising," the Redmond giant said in a press statement.

A Nokia spokesman called the complaint "frivolous," insisting that it was not abusing standards-essential patents and that Microsoft and Nokia manage their patent portfolios independently.

The EU is investigating Motorola Mobility, which was recently acquired by Google, for allegedly abusing standards-essential patents related to mobile phone technology.

Florian Mueller, a blogger with financial ties to Google's opponents, claims that the United States International Trade Commission has already dismissed similar charges.

Legal scholars have told Ars that patent thickets are uncharted territory for antitrust law. In an interview last year, Michael Carrier of Rutgers-Camden Law School pointed to potential collusion between Microsoft and Nokia as an antitrust trouble spot. However, he said, "the Department of Justice is sometimes slow to catch up to the realities of how patents are used in the industry." That might be why the fight is largely playing out in the European Union.