Communist Party of Britain chairman Bill Greenshields called today for a "mammoth turnout" for the People's Assembly Against Austerity in central London in June.
The event was announced on Wednesday and is expected to draw thousands to Westminster.
It aims to rally a broad front drawn from the labour movement, campaign groups and community organisations against the conservative coalition's cuts agenda.
Labour MP and People's Assembly Against Austerity supporter Katy Clark told the Star today that it would help "demonstrate to the public that there is a credible alternative."
The initiative, proposed by the Coalition of Resistance, has already won support from Unite, the RMT and other trade unions, the People's Charter, Labour MPs, the Green Party and a range of personalities in the arts, culture and intellectual life.
Mr Greenshields added: "The People's Assembly could mark an important new stage in building the militant mass movement needed to stop the Con-Dem austerity drive dead in its tracks,"
The assembly takes place at Central Hall in Westminster from 9.30am to 5pm on Saturday June 22.