The Federal Circuit held that 35 U.S.C. § 315(c) does not authorize petitioners to the Patent Trial and Appeal Board (PTAB) to join themselves as a party to an earlier filed inter partes review. CAFC also held that joinder of petitions may not be used as a means to add new issues to an earlier instituted inter partes review.
This is contrary to a PTAB Precedential Opinion Panel, Proppant Express Investments, from March 2019 which had indicated that parties can join their own petitions.
Read the case here.