Escalating talk across the political spectrum on containing tax deductions on interest payments on investment property loans may present a conundrum to borrowers and lenders.The Labor opposition over the weekend presented the most vigorous proposal, while one informed media report suggests the Government may also curtail use of this tax concession.Lenders are already under pressure to ration growth in supply of investment loans for prudential reasons and may face a clamp on demand in the medium term if these tax policy ideas take effect.Fairfax Media reported that Treasury is considering a universal cap on income tax deductions that would apply to negative gearing as well as employment-related expenses such as self-education, transport, union fees and work-related clothing.Arising out of the government's review into taxation, the proposal would abolish caps on specific expenses and replace them with an overall ceiling that would limit total deductions to a proportion of income or an indexed ceiling.In a speech to the NSW Labor Conference in Sydney on Saturday Opposition leader Bill Shorten said negative gearing would be available only on newly constructed houses and flats.Shorten said there would be "no change to negative gearing for existing negatively geared properties, grandfathering existing arrangements for those properties and investors currently accessing negative gearing."Labor also said the capital gains tax concession will be reduced from 50 per cent to 25 per cent, winding back half on one of the tax reforms of the Howard/Costello era."There will be no change to capital gains tax rules on existing assets and the family home, and personal superannuation will be 100% capital gains tax free," the Labor leader said.