Does a union have a duty not to discriminate impermissibly among its members?

Unions have a duty not to discriminate impermissibly among their members, but there is certainly "no requirement that unions treat their members identically as long as their actions are related to legitimate union objectives." Vaughn v. Air Line Pilots Ass'n , Int'l , 604 F.3d 703, 712 (2d Cir. 2010). A union's decision to discriminate against its members on an impermissible basis will violate the duty of fair representation only where the aggrieved members set forth "substantial evidence of discrimination that is intentional, severe, and unrelated to legitimate union objectives." Amalgamated Ass'n of St., Elec. Ry. & Motor Coach Emps. of Am. v. Lockridge , 403 U.S. 274, 301, 91 S.Ct. 1909, 29 L.Ed.2d 473 (1971).