The move is the latest salvo in a battle between the companies that started when Apple filed a lawsuit against HTC in March, charging it with infringing on 20 patents.
After Apple first filed suit against HTC, onlookers speculated that the suit was in fact aimed at Google, with which Apple appears to have an increasingly tense relationship.
Google created Android, the operating system that powers many of HTC's recent popular phones.
While Apple quickly gained mobile market share with its iPhone, it may be beginning to view Android as a threat.
A controversial report released this week by NPD showed that more Android phones may have sold last quarter than iPhones.
The report, however, was based on a survey of users rather than actual sales.
In addition to Apple's initial lawsuit, the company has also filed a complaint with the ITC, which in March agreed to investigate HTC.
See also: HTC defends itself in Apple lawsuit