ROME — The Italian government is to call a confidence vote on its 2014 budget that will test the strength of Prime Minister Enrico Letta's majority for the first time since Silvio Berlusconi's center-right threatened to quit the coalition.

Letta's government is virtually certain to survive with the support of the New Center Right party, which defected away from Berlusconi's Forza Italia earlier this month because it wanted to keep the government afloat.

But the vote, announced on Monday by Parliamentary Affairs Minister Dario Franceschini, could still the occasion in which Forza Italia definitively splits with Letta's center-left Democratic Party and moves into opposition.

Berlusconi has threatened as much ahead of a vote likely to expel him from the Senate this week.

The vote is just one part of the budget's passage through parliament, which must be completed by the end of the year.

Berlusconi had been expected go into opposition following his conviction for masterminding a tax-avoidance scheme at his Mediaset empire.

Confidence votes are often called to speed through legislation in the Italian parliament, but this one adds to rising tension ahead of the vote on Berlusconi's expulsion, a potential watershed in the career of the man who has dominated Italian politics for two decades.

Earlier on Monday Berlusconi described the expulsion vote as a "coup d'etat." Due to take place on Wednesday, the Senate vote could be rescheduled if budget negotiations run over.