Microsoft has lost the latest round in a patent-infringement case that could lead to an import ban on its phones.

Administrative Law Judge Theodore Essex of the U.S. International Trade Commission ruled on Monday that Nokia and Microsoft Mobile products infringed two patents held by R&D company InterDigital. Essex’s decision is preliminary and will be reviewed by the full commission, which is expected to announce its final ruling on Aug. 28. The final ruling could lead to a ban on importing the phones into the U.S.

The ruling covers most of Microsoft’s mobile phones, according to InterDigital spokesman Patrick Van de Wille. Microsoft acquired Nokia’s devices business last year. The patents in the case cover technologies involved in powering up a phone and having it connect to 3G wireless networks. Even though most current cellphones use 4G LTE, they still have 3G capability for use where 4G isn’t available.

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