Serious concerns have been expressed by US regulators who have said they are worried about the timing of new accounting rules that could potentially force banks to move more assets onto their balance sheet. The Financial Accounting Standards Board made changes in May to rules that could force banks to move more assets onto their books, and could affect trillions of dollars of off-balance-sheet assets when they take effect in 2010. Chairman of the Federal Deposit Insurance Corp Sheila Bair said the timing to implement the off-balance-sheet rules 'gives me some heartburn', Reuters reports. The US Comptroller of the Currency John Dugan also expressed concern during a Senate Banking Committee hearing about the timing, and said that regulators will issue guidance 'shortly' on how banks should account for the changes.