Apple vowed to appeal a $300 million royalty payment a US court ordered it to pay a patent management company after a retrial of a case involving standards-essential patents.

PanOptis Patent Management and various subsidiaries won a previous trial against Apple, which was originally ordered to pay $506 million before a retrial was ordered to allow a jury to rule on the sum.

The patent house purchased LTE-related patents from Samsung Electronics, LG Electronics and Panasonic which it claims Apple is using without a licence.

Patents covered by the dispute relate to technology considered essential for devices to connect to LTE networks. PanOptis Patent Management is seeking royalty payments, but is not looking to stop Apple from selling devices in the US.

PanOptis Patent Management filed its suit in a district court in Texas: a federal appeals court recently ruled plaintiffs cannot sue companies in areas in which the defendant doesn’t employ anyone and Apple subsequently closed its retail stores in the region.

Apple last month reportedly threatened to exit the UK market if a court orders a global royalty rate which could cost the iPhone maker up to $7 billion.