A U.S. district judge for the Southern District of California has ruled that Qualcomm Inc. must pay back almost $1 billion of patent royalty rebates to Apple Inc.

In a preliminary ruling, Judge Gonzalo Curiel said Qualcomm should make the payments to Apple as part of a 2013 business cooperation and patent agreement between the companies.

The decision will not become final until after the trial in the case, which begins in April, Reuters reported March 14.

Apple sued Qualcomm in 2017 for supposedly engaging in an "abusive" patent licensing model, resulting in the overcharging of billions. In response, the chipmaker claimed Apple breached contractual agreements, mischaracterized those agreements and misrepresented facts. Qualcomm also accused the tech giant of infringing on some of its patents for key technologies used in certain iPhone models.

Qualcomm is hoping to settle its dispute with Apple later this year.