Blackberry has filed a lawsuit in the US accusing Facebook of copying features from Blackberry Messenger in a violation of its patent rights.
Blackberry, which was once a leader in the smartphone market, says Facebook used the features and technology in its WhatsApp and Instagram apps.
The claims come after Blackberry has increased efforts to make money from its more than 40,000 patents.
Facebook has said it would fight the lawsuit.
Paul Grewal, deputy general counsel of Facebook, said Blackberry's claim "sadly reflects the current state of its messaging business".
"Having abandoned its efforts to innovate, Blackberry is now looking to tax the innovation of others. We intend to fight," he said.
Blackberry Messenger was the final hurrah of the failing Blackberry brand - a lightweight, simple program that was very popular, for a time, with young people. Particularly in the UK, where you may remember it was considered the tool of choice for rioters communicating during London's unrest in 2011.
BBM, as it was known, was indeed a precursor to popular apps like WhatsApp, but to say WhatsApp gained its popularity by stealing BBM tech is quite the stretch.
While Blackberry Messenger was (for a long time) locked to Blackberry device, WhatsApp wasn't. And while WhatsApp improved constantly, Blackberry Messenger, well, didn't.
Blackberry is claiming ownership over features that are so commonplace in mobile messaging you probably don't even consider them to be features. The little dot notifying you of a new message, for instance. Or the tiny icons that show that a message has been received and then read.
Blackberry, which was founded in Canada in 1984, was estimated to represent more than half of the smartphone market as recently as 2009, according to its lawsuit.
It introduced Blackberry Messenger in 2005 - more than six years before Facebook introduced a similar service, the lawsuit said.
Facebook owns WhatsApp and Instagram
In the filing, Blackberry claims Facebook has copied methods to notify users of new messages and tag people in photographs, among others. It says Facebook has been aware of its rights for years.
A spokeswoman for Blackberry said the company remains open to a partnership with Facebook.
"However, we have a strong claim that Facebook has infringed on our intellectual property, and after several years of dialogue, we also have an obligation to our shareholders to pursue appropriate legal remedies," she said.
Blackberry, which stopped making phones in 2016 after a dramatic sales decline, also filed a patent infringement suit against Nokia in February 2017. That case is pending.
The company has also settled disputes with other companies.