Nokia has thrown its support behind Apple's efforts to overturn a decision not to ban the sales of Samsung products that infringe on the iPhone-makers patents.
The Finnish handset maker, a rival of Apple, believes the recent decision to award Applebut could turn the US patent system into a "compulsory licensing" scheme.
The company challenges the decision by US District Court Judge Lucy Koh last December that a patent holder needs to prove a "causal nexus" between the patented feature and the source of demand for the infringing product.
Judge Koh rejected Apple's bid to ban 26 Samsung products on the basis of a few "narrow protected functions" included in Samsung's infringing products. Weighing up public interest, the more appropriate compensation wasshe originally awarded Apple.
Specifically, Apple had failed to "link any harm it suffers directly to Samsung's infringement" on a patent-by-patent basis. To win a permanent injunction, Apple would have needed to "show that consumers buy the infringing product specifically because it is equipped with the patented feature", Koh ruled.
Nokia's lawyers argue in a summary of the full brief (PDF) that the need to establish such a link "sets a dangerous precedent" that "could severely restrict, if not outright eliminate in some circumstances, the ability of a patent holder to obtain injunctive relief".
The precedent makes proving a causal nexus so burdensome it "may rarely, if ever, be met", and would force patent holders to license patented technology to competing firms, in turn harming incentives to innovate, according to Nokia.
Nokia is the only company to have supported Apple's bid to overturn the ruling, according to Reuters.
Separately, Judge Koh last week decided to cut Apple's damages award from $1.05bn to $450m, citing jury error.
Samsung's brief is not due for several weeks, after this happens 'friends of the court' (amici) that support its view are free to file their own.