Silvio Berlusconi's centre-right party said on Saturday that removing the former prime minister from parliament over a tax fraud conviction would be unacceptable and "unthinkable", escalating its row with centre-left coalition allies.
Angelino Alfano, secretary of Berlusconi's People of Freedom (PDL) warned Prime Minister Enrico Letta this week that the party could bring down the government if the centre-left Democratic Party (PD) voted to throw Berlusconi out, something PD members have repeatedly said they will do.
The Senate is due to vote in September on whether to expel the 76-year-old media mogul from parliament.
Alfano said on Saturday after a four-hour tactical meeting at Berlusconi's luxury villa near Milan that the PDL remained firmly united behind their leader.
"(Berlusconi's) removal from the office of senator is unthinkable and constitutionally unacceptable," he said.
His statement drew stern responses from PD members.
"The difficulties of the PDL are evident but you can't blackmail the government, because in a lawful state, laws are respected and sentences are applied," said Andrea Martella, PD vice president in the lower house.
Letta has said his government must focus on fostering Italy's recovery from recession and that Berlusconi's judicial problems will not affect the stability of his administration.
A Senate committee is due to begin hearing arguments on whether to eject Berlusconi on Sept. 9.
Berlusconi is desperately trying to find a way to stay in the political game despite a four-year jail sentence, commuted to one year, for a massive tax fraud at his Mediaset broadcasting empire.
He is expected to start serving the sentence, either under house arrest or doing social work, in mid-October.