A Canadian intellectual property licensing company on Monday accused Google in Delaware federal court of infringing the technology that underpins Siri.

In a 135-page complaint, WiLAN subsidiary IPA Technologies Inc. said that Google Assistant, the voice-activated personal assistant app, and other programs infringed six patents that it acquired from SRI International Inc. in May 2016.

The complaint marks a continued escalation of WiLAN's campaign targeting Silicon Valley's use of personal digital assistant technology.

It brings to 15 the number of big tech companies that have been challenged by the WiLAN subsidiary in the U.S. District Court for the District of Delaware.

According to the complaint, IPA acquired the patent portfolio in two tranches from SRI, a not-for-profit research institute that spun out Siri Inc. in 2007. Before that, SRI had led one of the world's largest artificial intelligence projects, which was funded by the Defense Advanced Research Projects Agency to “create groundbreaking software that could revolutionize how computers support decision-makers.”

SRI granted Siri a nonexclusive license to its patent portfolio in an effort to bring the personal digital assistant and speech-based navigation technology to the marketplace, IPA said in its complaint. The technology was demonstrated as an iPhone app at technology conferences and later released as an iPhone 3GS app in February 2010.

In April 2010, Apple Inc. acquired Siri Inc. and released the Siri personal digital assistant as an integrated feature of the iPhone 4S the following year.

IPA launched an initial round of lawsuits against Dell, HP Inc., Toshiba America Inc., Acer Inc. and ASUS Computer International in October 2016, about five months after it acquired the patents. All of those suits were settled within weeks of their filing.

But that December, IPA brought an infringement suit against Amazon.com Inc., whose personal digital assistant Alexa has become a leading product in the sector. The company has since filed similar cases against Acer, ASUS and a dozen other tech firms that either develop similar technology or incorporate it into their smartphones or tablets.

The defendants include tech heavyweights Sony Electronics Inc., Microsoft Corp., DISH Network Corp. and HTC Corp.

The most recent suit against Google claims direct, indirect and contributory infringement of six patents issued between 2003 and 2006. According to IPA, Google knew about the patented technology through the prosecution of other patents and patent applications.

“When the Google Assistant is initiated, it provides users with instructions (both audio and text) and examples of how to engage and operate Google Assistant in an infringing manner,” attorneys for IPA wrote. “As a further example, defendant instructs users on how to use the infringing products to perform speech-based navigation of an electronic data source.”

Google did not immediately respond Tuesday to a call seeking comment on the lawsuit.

IPA claims jurisdiction in Delaware under the state's long-arm statute. Acer, Amazon and Sony have all moved to dismiss similar lawsuits, arguing that IPA's patents were invalid because they were directed at patent-ineligible subject matter.

Meanwhile, other companies, including ASUS, have asserted affirmative defenses that run the gambit from invalidity and failure to state a claim to noninfringement and unenforceability. ASUS has also argued that venue in Delaware is improper because it lacks sufficient connections to the First State.

IPA is represented by Stephen B. Brauerman and Sara E. Bussiere of Bayard P.A.

The case, captioned IPA Technologies v. Google, has not been assigned to a judge. However, U.S. District Judge Richard G. Andrews of the District of Delaware is handling the other 14 cases.