The Greek government rejected Tuesday a call by three left-wing opposition parties to hold a referendum on the new European Union constitution, just hours before the treaty was to go before Greece's parliament for ratification.

The conservative government "thinks that there is no reason to hold a referendum after the expected ratification of the European Constitution by the national parliament," said a government spokesman, Evangelos Antonaros.

The 300 members of the Greek parliament were expected to start the debate on ratification Tuesday evening and it was expected to last three or five days depending on the number of lawmakers who want to take part in the debate.

The two main Greek parties, the ruling New Democratic Party and Pasok, the socialist opposition, which represent about 90 percent of the electorate, have both come out in favor of the new EU constitution, Antonaros said.

Relations between Greece and the EU "have always been handled by the parliament, that's the Greek way," the spokesman said.

However, on Monday, Pasok along with the Communist party KKE and another small leftist group Syn, called for a referendum. Pasok said it wanted to put the constitution before Greek voters for "educational" reasons. The other two leftist parties are opposed to the constitution.