Governing body World Rugby announced a three-man independent judicial committee after both the Rugby Football Union and the RBS Six Nations had taken no further action.
Marler was heard calling Lee “Gypsy boy” in England’s 25-21 win over Wales on 12 March.
Marler apologised to Lee at half-time and was reprimanded by England head coach Eddie Jones, but the decision not to sanction him caused an outcry and he now faces a retrospective ban.
Marler came off the bench in the 31-21 victory over France in Paris that secured England’s first Grand Slam since 2003, and returned to club action with Harlequins on Saturday.
The committee will comprise Terry Willis (chair, Australia), Jean-Noel Couraud (France) and Alan Hudson (Canada).