French phone equipment firm Alcatel has sued Microsoft, accusing it of infringing seven of its patents.
Alcatel is set to take over US-based Lucent Technologies
Alcatel has not revealed which Microsoft products it believes are in breach but says they relate to digital video and network communication.
It said the action, lodged in the US District Court for Eastern Texas was to protect its intellectual property.
The French firm added it hoped to resolve issues "through discussions rather than the courts".
Microsoft said that the suits appeared to relate to a long-running dispute between it and US-based Lucent Technologies which Alcatel is set to take over.