The 38-year-old leftist said he would mobilise his lawmakers and supporters against the measures to prevent them from causing irreparable harm to Greece's economy, after more than two years of austerity measures that have slashed wages by a third.
The time to stop the catastrophe is now," Tsipras said in a speech in the northern city of Thessaloniki. "These measures must not pass. They will deliver the final blow to the people."
The only way for Greece to cope with its spiralling debt was to repudiate a large part of it, Tsipras said: "That's the only credible and viable way to way to get out of recession."