Canadian telecommunications company Mitel Networks is suing Facebook over patents for “pro-active features for telephony” and an “automatic web page generator,” according to a filing.

The challenge comes a week after Yahoo filed suit over 10 patents it claims the social network violated. These legal issues could set back the initial public offering Facebook planned to make later this spring.

The company acknowledged its intellectual property risks in its most recent regulatory filing. “As we face increasing competition and gain an increasingly high profile, including in connection with our initial public offering, we expect the number of patent and other intellectual property claims against us to grow.”

In the latest suit, Mitel claims Facebook infringes on a patent for a method of automatic generation of a web page directory, as well as a patent covering systems for pro-actively suggesting communication features to users. Mitel says it sent Facebook letters in July 2011 and September 2011 identifying the patents and offering to discuss licensing arrangements, but Facebook did not respond.

Facebook declined to comment on the lawsuit and patents in question.