Several older Apple iPhone and iPad models infringe on a patent held by Samsung, a judge at the U.S. International Trade Commission said on Tuesday.
As part of the ruling, the ITC has issued a limited order to bar those devices from sale in the U.S.
The decision is final, however Apple can appeal it to the Federal Circuit, or bid for a reprieve from the White House, which has the power to approve or disprove of the ruling.
"We believe the ITC's Final Determination has confirmed Apple's history of free-riding on Samsung's technological innovations," Samsung said in a statement. "Our decades of research and development in mobile technologies will continue, and we will continue to offer innovative products to consumers in the United States."
Apple said it was disappointed in the ruling and plans to appeal it.
"We are disappointed that the commission has overturned an earlier ruling and we plan to appeal," Apple spokeswoman Kristin Huguet said in a statement. "Today's decision has no impact on the availability of Apple products in the United States."
The company added that Samsung was "using a strategy which has been rejected by courts and regulators around the world."
Samsung originally filed the case against Apple in June, 2011 -- some two months after Apple sued it, beginning the all-out legal war between the two tech giants. In the lawsuit, Samsung accused Apple of infringing on several of its patents, and sought import bans on certain iPhones, iPods, and iPads.
Tuesday's decision was originally expected last week, though was delayed several other times.
Even with the ruling, Apple still has some legal tricks it can play, says Kevin Taylor, a partner at the firm Schnader. "They can ask the court for a stay on this order pending an appeal," Taylor said. "It's not unusual to have that, especially in this case where a ban would be disruptive."
The case is separate from a complaint lodged against Samsung by Apple, accusing Samsung of infringing on several Apple patents. An initial ruling found Samsung infringing on four of Apple's patents, though a final ruling in that matter isn't due until August 1st.
Technology companies in recent years have increasingly turned to the ITC to settle their disputes. Companies can pursue an ITC case in parallel with civil lawsuits, and the threat of an embargo on products typically forces companies to settle more quickly. However, in the case of Apple and Samsung, the two companies have continued to fight through to the end.
This particular case is just one of many fights between the two companies, which are facing off in courts around the world. Despite that, the two continue to do business with one another, with Samsung supplying several key components used in Apple's products.
The public version of the ruling is below:
Update, 3:27 p.m. PT: Adds statement from Samsung. Update at 4:35 p.m. PT adds statement from Apple, and additional background on gravity of the decision.