Therese Serignese and Linda Traitz, both from Florida, are joining a lawsuit that was filed last month by Tamara Green. The plaintiffs contend that statements from Cosby's lawyer, Martin Singer, in response to their claims have publicly branded them liars.
All three women say Cosby assaulted them in the 1970s after giving them drugs.
The number of women who have made similar claims against Cosby now stands at more than 20, but Cosby has flatly denied the accusations through Singer. Last month, Cosby reportedly hired private investigators to dig up dirt on his accusers.