Rome, August 13 - If Italian President Giorgio Napolitano were to grant any sort of pardon to ex-premier Silvio Berlusconi in his current legal troubles, it would be grounds for impeachment, a 5-Star Movement (M5S) politician said Tuesday. Mario Giarrusso, a Senator with the maverick M5S led by comedian Beppe Grillo, wrote on his Facebook page that Napolitano would be headed for serious trouble if he granted amnesty to Berlusconi, whose conviction for tax fraud was upheld last week by Italy's highest appeals court. "If Napolitano were to grant (a pardon) to Berlusconi or any other act of clemency that would take away from his known criminal responsibility, it would be a subversive act," for which Napolitano should be impeached, wrote Giarrusso. Some supporters of Berlusconi and his People of Freedom (PdL) party have demanded that he be pardoned for his conviction, arguing that he has long been the victim of malicious prosecution. They've even threatened to bring down Italy's fragile coalition government, which has brought together the PdL and the Democratic Party (PD), over the issue. That has led some to suggest that Berlusconi should be pardoned from his sentence, even though a 2012 anti-corruption law makes people who have received definitive criminal convictions ineligible to run in future elections or hold public office. The courts are still reviewing the political ban. And although Berlusconi was also sentenced to four years in prison, he is not in danger of actually being jailed because he is well over 70 and will be given the option of serving the remaining year of the sentence under house arrest or doing community service. Napolitano, 88, reluctantly agreed to become Italy's first head of State to be re-elected in April as the parties were unable to agree on a successor, amid chaos after February's general election failed to produce a clear winner.