Wells determined that 8 of the allegations were substantiated and that Bird's continued behavior had caused a risk of health and safety for Roberts, who had sought psychological treatment for work-related stress.
"This action by Mrs Bird evinces a lack of emotional maturity and is indicative of unreasonable behavior, the likes of which I have already made findings on," Wells said in her decision.
The ruling does not mean that unfriending a colleague automatically constitutes bullying, but that the act could prove a pattern of unreasonable and hostile behaviors.
"Actions on social media, especially cyberbullying could certainly be used to substantiate a claim for harassment based on a hostile work environment," Ted Geiger, a New York attorney specializing in civil litigation, told CNBC.
"This decision here is a onetime decision and while the unfriending is the headline, since the decision was based on number of actions over a two year period…I don't think that unfriending will become the sole basis for liability anytime soon."
Facebook did not immediately respond to a request for comment.