A federal trade commission voted today to investigate Creative Technology's claims that Apple infringed on its patent for its MP3 players' user interface, heightening the tension in a dispute that has already seen three lawsuits filed.

The patent battle begins.

The US International Trade Commission voted to probe Creative's allegations that the user interface in Apple's vaunted line of portable music players--the iPod, iPod Nano, and iPod Mini--infringes on its "Zen Patent," which covers the user interface in Creative's Nomad and Zen portable digital media players.

Creative filed a complaint with the commission earlier this month when it filed a related lawsuit against Apple, seeking an injunction to prevent Apple from importing iPods from China, where they are manufactured.

Apple has since countersued in both Wisconsin and Texas, claiming that Creative's players violate three of its own patents for the display of computer data, editing device data on a computer, and the use of certain computer icons.

The commission's vote in no way determines wrongdoing in the case. It was assigned to commission administrative law judge Paul Luckern, who will likely hold an evidentiary hearing in the next several months. A final commission ruling in the matter is not expected for at least a year.

Industry experts have said this battle could come down to whether Creative is able to survive what will likely be a long, exhausting court fight. The company trails far behind Apple in the MP3 player market, and it continues to lose money.

Apple shares were down 65 cents, or 1.1 percent, to $57.68, while shares in Creative were up 24 cents, or 5 percent, to $4.96.