Rome, July 23 - Premier Enrico Letta on Tuesday vowed that his government would press ahead with a bill to phase out public funding for political parties. The bill faces a tough passage through parliament after over 150 amendments were presented to it. But Letta, whose executive is based on a fragile alliance between his centre-left Democratic Party (PD) and ex-premier Silvio Berlusconi's centre-right People of Freedom (PdL) party, is determined to push the legislation through. "We won't take steps back on the abolition of public financing of parties," Letta said via his Twitter account, @EnricoLetta. "The bill we presented is a good reform. Why block it?". If the bill is approved, party funding will be reduced to 60% of its current level in the first year, 50% in the second year 50% and 40% in the third year before being abolished altogether. The issue of party funding is high up on the political agenda in part thanks to the anti-establishment 5-Star Movement (M5S), which won about a quarter of the vote in February elections and refuses to accept public financing of any kind. M5S leader Beppe Grillo tapped into widespread public disenchantment as he berated the misuse of public money following a series of corruption scandals involving parties across the political spectrum. The M5S called the government's bill a "moral victory" but also dubbed it a "scam law" for a mechanism it contains that enables people to donate a small slice of their taxes to parties. As part of this, an individual taxpayer's money will be split among parties automatically unless the person explicitly declares on their tax return that it should not go to a political party. As the bill stands, the money would be divided proportionally among all parties.