The expulsion of Montoneros from Plaza de Mayo was a key event of the third presidency of Juan Pern. It took place on May 1, 1974, during celebrations of International Workers' Day.

Montoneros (Spanish: Movimiento Peronista Montonero-MPM) was an Argentine left-wing peronist guerrilla organization, active during the 1960s and 1970s. The name is an allusion to the 19th-century cavalry militias called Montoneras, who fought for the Federalist Party during the Argentine Civil Wars.

After Juan Perón's return from 18 years of exile and the 1973 Ezeiza massacre, which marked the definitive split between left and right-wing Peronism, the president expelled the Montoneros from the Justicialist party in May 1974. The group was completely destroyed during the Dirty War.