This news is just rumor for now, so take from it what you will. In an advertisement for the Mass Effect 3 N7 Collector's Edition, Eurogamer spotted mention of an "online multiplayer pass." This could mean that Mass Effect 3 will receive a standalone mulitplayer component, perhaps the previously rumored four player co-op mode. That co-op mode is said to feature "competitive elements," which will include some original missions designed just for the online play. BioWare co-founder Dr. Ray Muzyka told EuroGamer that multiplayer is something being explored in all of his company's games, so it does not seem like too much of a stretch to see an online co-op mode appear in Mass Effect 3. This is all just rumor for now, so until something gets confirmed closer to ME3's launch date, take the information with a grain of salt. There is supposed to be a Mass Effect announcement later this month, so maybe this rumor of a multiplayer component will be confirmed.
Mass Effect 3 launches on March 6th, 2012, for the PC, PS3, and 360.