Greece's most famous living composer, Mikis Theodorakis, is calling the terms of last year's massive economic bailout a "national betrayal."
Theodorakis, best known for the score to the film Zorba the Greek, spoke to 20,000 protesters in central Athens Tuesday. The marchers oppose any more international bailouts for Greece's struggling economy.
Theodorakis urged the opposition not to join the government in accepting further economic reforms.
The Greek economy is still in shambles even after last year's $158 billion rescue package from the European Union and International Monetary Fund.
Some EU officials say they are considering another bailout, but only if the Greek government and opposition can agree on more austerity measures.
Athens has already said it will sell off some state-owned assets to help pay down the debt.
Opponents to any more government spending cuts have been holding daily protests in cities across Greece.
Some information for this report was provided by AP and Reuters.