Facebook has filed a countersuit claiming Canadian telecommunications company Mitel Networks is infringing on patents it now owns, The Next Web reports.

The social network alleges that Mitel infringes on its patents for a “telephone status notification system” and “user definable on-line co-user lists.” These are both patents that Facebook bought from Microsoft a month after Mitel’s initial patent suit was filed. The patents were originally owned by AOL, but the company sold them to Microsoft in April.

In March, Mitel filed suit against Facebook over patents for “pro-active features for telephony” and an “automatic web page generator.” The challenge came a week after Yahoo filed suit over 10 patents it claims the social network violated. Facebook ended up countersuing Yahoo as well, but the companies came to a settlement last month that includes cross-licensing their patent portfolios and a new advertising partnership.

It is unclear whether Facebook will pursue a similar patent-sharing deal with Mitel. The social network has also filed a motion to dismiss Mitel’s initial lawsuit.