In another blow to Android, a judge at the International Trade Commission has issued an initial determination that Motorola Mobility infringes four claims of a Microsoft patent.
The judge also found that Motorola does not infringe claims related to six other Microsoft patents.
The notice follows an ITC decision on Monday to ban the importation of HTC Android products that infringe an Apple patent.
In a statement, Microsoft said it was pleased with the finding. It referred to Samsung, HTC, Acer and others as choosing "the right path forward" in deciding to license patents from Microsoft.
"One key step behind us in the ITC. More to follow. But we'll also remain focused on licensing," Brad Smith, general counsel at Microsoft, wrote on Twitter.
Motorola, which has agreed to be acquired by Google, was one of the few large phone makers to battle Microsoft over mobile patents related to Android rather than sign a licensing deal. It did not immediately reply to a request for comment about the ITC notice. Motorola can now ask the full commission to review the initial determination.
Microsoft has declined to disclose which patents it has licensed to Android device makers, so it's unclear if it has been signing agreements for the patents that the ITC found Motorola is not infringing.
Patent number 6,370,566, which the administrative law judge at the ITC found Motorola infringes, describes generating meeting requests and group scheduling from a mobile device.
Android is being attacked in courts around the globe. In addition to Microsoft's actions, Apple has sued Samsung and Motorola in various courts over their Android products. In addition, Oracle is suing Google for patent infringement in Android.