Socialist party PASOK, the junior partner in the previous coalition government, called for Tsipras's resignation.
"Since Mr. Tsipras is unable to take responsible decisions, he ought to resign and let citizens vote for their future via elections," PASOK's leader Fofi Genimmata said in a statement.
Centrist To Potami party blasted the leftist prime minister for his decision to call a referendum, saying it would fight to keep the country in the heart of Europe.
"Alexis Tsipras and (Independent Greeks leader) Panos Kammenos decided to lead the lobby of the drachma, to take the country out of the European Union and push it over the cliff," the party's leader Stavros Theodorakis said in a statement.
"We will fight together for a strong Greece in the heart of Europe."
Conservative New Democracy said the government brought the country to an impasse, isolating it from Europe, accusing Tsipras for throwing the responsibility he himself could not bear to the shoulders of the people.
"Mr. Tsipras today leads the country to a referendum with a the ultimate question being a yes or no to Europe and he proposes a rift with all our partners and an exit from the euro," former prime minister Antonis Samaras said.
(Reporting By Michele Kambas and George Georgiopoulos)
