The Movement of Socialist Affirmation (Spanish: Movimiento de Afirmación Socialista) was formed in 1989 by left christian elements of IU. Leaders included Henry Pease, Rolando Ames and Gloria Helfer. It worked within IU in the 1989 and 1990 elections. In 1992 it broke with IU, and was one of the organizations founding MDI. MAS worked with MDI in the 1992 and 1993 elections. In the 1993 referendum, it supported the No.
MAS is no longer functioning.