Rome, May 17 - A government reform of the unpopular IMU property tax will cover businesses as well as homes, Premier Enrico Letta said Friday. Ex-premier Silvio Berlusconi threatened to pull the plug on Letta's fledgling right-left government unless firms got IMU breaks too. Letta, of the centre-left Democratic Party (PD), had previously said the postponement of a June IMU instalment would only be for first homes, angering Berlusconi's People of Freedom (PdL) party. The premier has said the postponement is a holding move ahead of a "comprehensive" rejigging of the unpopular tax to help the worst-off. Berlusconi made an election pledge to scrap IMU entirely and pay back last year's take.