The much-maligned rice program is critical to Yingluck's support base in the poorer north and northeast.Generous subsidies for farmers were a centerpiece of the platform that swept her to power in 2011, but they have left Thailand with vast stockpiles of rice and a bill it is struggling to fund.Opposition leaders say the scheme is riven with graft. Losses to the taxpayer, estimated at 200 billion baht ($6 billion) a year, have fuelled urban anger with Yingluck. She and her government are being investigated by an anti-corruption panel for alleged irregularities in the subsidy scheme.The farmers' anger over not being paid and the investigation into the subsidy program come as Yingluck faces a campaign of street protests to oust her that has been going on for nearly four months.Four protesters and a police officer were killed on Tuesday when police attempted to reclaim protest sites near government buildings that have been occupied for weeks.The protesters want to stamp out what they see as the malign influence of Thaksin, regarded by many as the real power behind the government. This week they targeted businesses linked to the Shinawatra family, sending their stock prices lower.Property developer SC Asset Corp has lost almost 10 percent since Wednesday and mobile handset distributor M-Link Asia Corp has lost 12 percent. The protests are the latest installment of an eight-year political battle broadly pitting the Bangkok middle class and royalist establishment against the mostly rural supporters of Yingluck and Thaksin. Demonstrators accuse Thaksin of nepotism and corruption and say that, prior to being toppled by the army, he used taxpayers' money for populist subsidies such as the rice scheme and easy loans that bought him the loyalty of millions.