Apple might have to pay $862m in damages after a Wisconsin jury ruled that the iPhone maker had used a technology owned by the University of Wisconsin-Madison without its permission.

The Wisconsin Alumni Research Foundation (WARF), an independent nonprofit technology transfer organisation serving the University of Wisconsin, sued Apple in 2014 claiming infringement of a 1998 patent for improving chip efficiency.

The case revolves around the usage of the technology in iPhone 5s, iPhone 6 and iPhone 6 Plus.

Last month, WARF filed a new lawsuit claiming that Apple is still using the technology in its newly launched 6S and 6S Plus.

In the court papers, the university claims that it offered Apple to license the patent, which would have allowed the company to use the technology without any interruption, but Apple declined the offer.

By ignoring the offer, Apple willfully infringed the patent which led to the lawsuit and could cost Apple up to $862m in damages.

However, Apple has denied any infringement and said that the patent is invalid.

The iPhone maker tried to convince the US Patent and Trademark Office to review the patent’s validity, but the request was rejected by the agency in April.

This is not the first time that WARF has sued a tech giant for the patent, as in 2008 it slapped Intel with a lawsuit for infringement of the same patent.

However, the case was settled out of court on the following year on the eve of trial.