Apple has taken legal action against phone maker HTC, alleging it has infringed patented technology.
HTC has been accused of infringing 20 patents owned by Apple that are used in the iPhone.
Apple said the patent infringements covered technology used in the iPhone interface as well as its "underlying hardware and architecture."
HTC makes phones for many firms including Google and was behind the Nexus One handset.
In a statement Apple boss Steve Jobs said: "We can sit by and watch competitors steal our patented inventions, or we can do something about it.
"We've decided to do something about it," he said. "We think competition is healthy, but competitors should create their own original technology, not steal ours."
In its legal filing, Apple is seeking a lasting injunction which would effectively bar HTC from selling phones that use the disputed technology in the US.
The legal action has been filed with the US International Trade Commission and a district court in Delaware.
In its response to the legal action, HTC said it had only just learned about Apple's legal action and has not had the chance to investigate the filing.
"Until we have had this opportunity, we are unable to comment on the validity of the claims being made against HTC," it said in a statement.
In addition to making the Nexus One, the first handset to be branded by Google, HTC has also made several handsets that use Google's Android operating system.
At the same time Apple is locked in legal action with Nokia. The Finnish phone giant sued Apple for patent infringement in October 2009, alleging it had stolen patented technology.
In response, Apple countersued in December 2009. Nokia launched a second round of legal action in the closing days of 2009.