Last week, the same action was taken against Samsung, citing five patents Apple holds. HTC has its counter-claims suit against Apple, too, from back in May, which asks for banning Apple's products. Samsung, in its turn, also filed its own complaint with the ITC, withdrawing from the lawsuit in California. The reason to go to the ITC is that the commission's cases take months for a verdict, as opposed to years with other courts.
Of course, these lawsuits are extremely unlikely to end with a ban, only some sort of settlement between the parties involved, but you never know which side of the bed will the judges wake up on the given morning. The mobile industry patents game is so red hot lately, that even the Feds are supposedly looking into the Nortel patent deal, where a consortium of six companies (Apple is one of them), that usually compete, won the bid paying five times what Google offered initially.
Back in April the ITC staff sided with HTC for the first complaint, which was filed by Apple in March, which likely means a defeat for the first case when the results come August 5th; that might be the reason Apple is filing another one now, since HTC might get some patent protection with its purchase of S3 last week. The ITC already backed Nokia against Apple, which had to settle, resulting in a nice chunk of cash for the Finns, plus recurring payments from each iPhone sold, but, of course, Nokia's patent portfolio is much stronger than HTC's.