The smartphone manufacturer HTC says it will "vigorously fight" a court ruling in favour of its rival Apple that could ultimately lead to a ban on US imports of Google Android phones and tablets.
Apple had accused the Taiwan-based company of infringing ten of its patents and taken the case to the International Trade Commission.
Six of the charges were dropped, but in a preliminary ruling the judge ruled that HTC had infringed two of the remaining four.
The ruling is due for a final review in December. But shares in HTC have fallen after Citigroup pointed out that initial verdicts by the ITC are rarely overturned.
Potentially the company may redesign its technology or pay license fees to Apple. In a worst-case scenario for HTC, technology industry analysts say all of its Android-based products could be barred from the US market.
Android phones and tablets made by other companies could even be affected as well.
HTC is vowing to contest the decision. Spokeswoman Grace Lei said: "We are highly confident we have a strong case for the ITC appeals process and are fully prepared to defend ourselves using all means possible."
Apple's share of the smartphone market has slipped over the past 12 months. Sales of the iPhone have now been overtaken by both Android handsets and Blackberry devices.
But, with a new iPhone due to be released later this year, Apple will be buoyed by the ITC ruling, which appears to leave its strongest competitor significantly weaker.