Berlusconi's swan song may not be easy listening for Letta

September has come, and summer is (almost) over - but the heat won't leave Italy for a bit. The Italian Senate's Immunities Committee has begun debating whether to strip Silvio Berlusconi of his seat as a result of his recent tax fraud conviction. As we wrote on this blog several times (see here, here and here), the outcome of the vote that will follow this debate could be decisive for the future of Prime Minister Enrico Letta's shaky coalition government.

A quick recap:

• Under Italy's new anti-corruption law, Berlusconi won't be able to stand for election for the next six years due to his tax fraud conviction. As we said, he also risks losing his seat in the Italian Senate.

• Berlusconi's PdL party wants to delay the vote in the Senate's Immunities Committee, arguing that the opinion of the Italian Constitutional Court and the ECJ should be sought first. The legal reasoning behind the request is that, according to Berlusconi's party, the anti-corruption law can't be applied retroactively - that is, it doesn't cover crimes committed before its entry into force in December 2012. The problem is the other parties (including Mr Letta's Democratic Party, currently in government with Berlusconi's PdL) are not on the same wavelength and want to wrap everything up as quickly as possible.

• A preliminary vote on the request to refer the matter to the Constitutional Court and the ECJ could take place tonight or tomorrow. It remains unclear when the final vote will happen. However, several key members of Berlusconi's party have made clear that, if the Committee refuses to delay the final vote, it will be the end of the coalition with Mr Letta's Democratic Party.

In other words, Italy seems to be heading towards fresh political instability. If the existing coalition collapsed, snap elections would become a concrete possibility - but not the only one. The ball would once again be in the court of Italian President Giorgio Napolitano, who would presumably try and put together an alternative majority (with the help of 'rebel' Senators from Beppe Grillo's Five-Star Movement and Berlusconi's party) before throwing the towel in and dissolving parliament.