Miners BHP Billiton and Xstrata have reacted angrily to the Australian government's plans to introduce a new resource rent tax and say the levy may jeopardise future investments. PM Kevin Rudd wants to slap a 40% tax on resource projects from July 2012, which could raise about A$12bn ($11bn) in the first two years. BHP said the new tax would increase the total effective tax rate on the group's profits earned from its Australian operations from 43% to 57% from 2013.Rio Tinto, which like BHP has extensive iron ore operations in Australia's Pilbara region, is also lower.Elsewhere in commodities, oil stocks are lower. BP is down heavily as the oil leak in the Gulf of Mexico shows no sign of abating. It has denied responsibility for the rig explosion that caused the problems, but expects to meet the clean-up costs that are now being estimated in the tens of billions. Other oil groups are down in sympathy.Fellow sector giants Shell and BG Group are also suffering.Top performing sectors so far todayHealth Care Equipment & Services 3,794.17 +1.67%Tobacco 25,054.68 +1.47%Chemicals 5,389.45 +1.40%Pharmaceuticals & Biotechnology 8,668.23 +1.03%Food & Drug Retailers 4,957.96 +1.00%Bottom performing sectors so far todayIndustrial Metals & Mining 6,500.03 -3.54%Oil & Gas Producers 8,082.80 -3.22%Mining 21,463.81 -3.11%Life Insurance 3,614.54 -1.81%Banks 4,979.39 -1.49%