Ribbon Communications has broken its silence on Metaswitch Networks‘ federal antitrust lawsuit alleging it is “systematically eliminating” competition to raise prices for network operators.

Last week, Metaswitch said it had filed the suit in the U.S. District Court for the Southern District of New York. The company said it is Ribbon’s only significant remaining competitor in the United States and Canada that competes to “transform and modernize” landline telephone networks for VoIP in many communities. The lawsuit alleges that Ribbon has “aggressively consolidated the industry through serial acquisitions and is illegally using exclusionary and deceptive tactics to eliminate its last major competitor in the market.”

Ribbon said the suit is Metaswitch’s “latest litigation tactic to try to avoid payment for its use of Ribbon’s intellectual property.” Metaswitch wouldn’t comment on Ribbon’s response to its suit.

Ribbon’s Franklin Hobbs

“It is disappointing that Metaswitch is attempting to relitigate claims that it already lost in federal court,” said Franklin Hobbs, Ribbon’s CEO. “Ribbon will not be deterred by these actions, and we look forward to having Ribbon’s intellectual property rights vindicated and Metaswitch finally paying for its misappropriation of Ribbon technology.”

Ribbon originally filed a patent lawsuit against Metaswitch in 2014, and that suit resulted in a jury verdict finding that Metaswitch “infringed seven Ribbon patents and owed damages to Ribbon.” In a follow-on lawsuit, Ribbon contends that, despite the jury verdict, Metaswitch continues to “use Ribbon’s patented technology and owes damages for that ongoing use.”

Ribbon also contends, in a separate lawsuit pending in Texas state court, that Metaswitch has been engaged in an “orchestrated campaign to steal and use Ribbon’s trade secrets,” and that lawsuit is set for trial in April 2019. This past March, Ribbon brought two other patent lawsuits claiming Metaswitch’s unauthorized use of 10 additional Ribbon patents.

Ribbon said Metaswitch’s most recent lawsuit, “under the guise of antitrust violations, attacks Ribbon for bringing suits to protect Ribbon intellectual property rights, even though the Supreme Court has made clear that such suits are protected by the First Amendment and immune from antitrust scrutiny.” It also “rehashes allegations that it previously lost in federal court and complains of a Ribbon merger that the federal government already cleared from an antitrust perspective,” according to Ribbon.

Ribbon says it “defeated” Metaswitch’s claims in earlier cases, including Metaswitch’s claims alleging that Ribbon infringed Metaswitch patents, and Ribbon “will vigorously defend itself against Metaswitch’s latest claims.”