Silvio Berlusconi has used a much-awaited video message to the nation ahead of a Senate vote to oust him from parliament to relaunch his first political venture - Forza Italia (Go Italy!) - in a signal that he is ready to pull support from the government.

Although his current People of Freedom (PDL) party is joined in a ruling coalition with the centre-left Democratic party (PD), the former prime minister urged his supporters to back him in his fight against the left.

"I'm here to ask every one of you to open your eyes and take the field to fight the left," Berlusconi said in the 16-minute video message.

He called for Italians to vote for him although there are no elections in sight, unless the PDL drops out of the coalition. Berlusconi pledged to lower taxes and reform the judicial system if he were even given the mandate again.

The video was aired a few hours before a Senate panel met to decide whether he should lose his seat in the upper chamber. The move is based on a 2012 anti-corruption law stipulating that anyone convicted to more than two years in prison cannot hold or run for office.

Italy's top court upheld a four-year jail sentence for tax fraud against Berlusconi.

But Berlusconi said that whatever the decision, he would continue in politics.

"I will always be with you, at your side, expelled from parliament or not," he said. "It is not the seat that makes a leader but people's support."

PDL MPs have repeatedly said that they would pull out of the government if PD members voted against their leader.

Berlusconi lashed out at judges who convicted him in August, claiming that charges against him were politically motivated and part of a larger leftist plan to turn Italy into a socialist country.

The 76-year-old described Italy as a "halved democracy".

"We do not want Italy to remain caged behind the bars of a sick justice," he said. "This is why I've decided to pick up again the flag of Forza Italia."

About 24 hours before that announcement an official Forza Italia account was created on Twitter.

Forza Italia - Go Italy - was Berlusconi's first political venture, evolving into PDL in 2009.

PD secretary Guglielmo Epifani described the video message as "irresponsible".