The U.S. Treasury and Internal Revenue Service have changed the "use it or lose it" rule on flexible spending accounts to allow employees covered by those plans to carry over up to $500 in unused account balances, Business Insurance reported.  The modification of the 29-year-old rule by the U.S. Treasury and Internal Revenue Service is intended to reduce "wasteful" flex spending by employees under pressure to use up their account balances. Under the revised rule, employers will have a choice between either allowing employees to carry over up to $500 or offering a 2 1/2-month grace period in which employees can spend unused balances. An estimated $14 million families currently participate in flexible spending accounts to set aside pre-tax dollars to pay health care expenses.