Left Opposition of PCE (in Spanish: Oposición de Izquierda del PCE) was initially founded as an internal tendency within the Communist Party of Spain (PCE), but later evolved into an independent formation. It started publishing Voz comunista in 1973.
OPI-PCE promoted abstention in the 1976 referendum. In 1977 OPI-PCE founded the Workers Communist Party (PCT).
References
Left Opposition of PCE Wikipedia(Text) CC BY-SA