The 2007 Energy Independence and Security Act also instructed NHTSA to establish a credit trading and transferring scheme to allow manufacturers to transfer credits between categories, as well as sell them to other manufacturers or non-manufacturers. In addition, the period over which credits could be carried forward was extended from three years to five. Traded or transferred credits may not be used to meet the minimum standard in the domestic passenger car fleet, however they may be used to meet the "attribute standard". This latter allowance has drawn criticism from the UAW which fears it will lead manufacturers to increase the importation of small cars to offset shortfalls in the domestic market.