(Reuters) -GlaxoSmithKline sued Pfizer ( PFE ) and BioNTech in Delaware federal court on Thursday, accusing them of infringing GSK patents related to messenger RNA (mRNA) technology in the companies' blockbuster COVID-19 vaccines.

GSK said in the lawsuit that Pfizer ( PFE ) and BioNTech's Comirnaty vaccines violate the company's patent rights in mRNA-vaccine innovations developed "more than a decade before" the outbreak of the COVID-19 pandemic.

A Pfizer ( PFE ) spokesperson said in a statement that the company is "confident in our IP position around Comirnaty" and intends to "vigorously defend" against GSK's claims. Representatives for BioNTech and GSK did not immediately respond to requests for comment on the lawsuit.

The lawsuit adds to a web of high-stakes U.S. court cases involving Pfizer ( PFE ), BioNTech and Moderna over patent royalties for technology used in their vaccines, including a case brought by Moderna against Pfizer ( PFE ) in 2022.

Pfizer ( PFE ) made $11.2 billion from sales of Comirnaty last year, while Moderna earned $6.7 billion in revenue from its vaccine Spikevax. Sales of both vaccines declined significantly last year from 2022.

GSK also sued Pfizer ( PFE ) for patent infringement last year over technology used in Pfizer's ( PFE ) respiratory syncytial virus (RSV) vaccine Abrysvo. Pfizer ( PFE ) has denied GSK's claims in that case.