WASHINGTON, May 19 (Reuters) - The U.S. Transportation Department is expected to declare that fuel economy rules issued under then President Joe Biden exceeded the government's legal authority by including electric vehicles in setting the rules, automakers said on Monday. Transportation Secretary Sean Duffy said the department's National Highway Traffic Safety Administration on Friday submitted its interpretive rule, "Resetting the Corporate Average Fuel Economy Program" to the White House for review. He said in a statement the prior administration had "illegally used CAFE standards as a backdoor electric vehicle mandate – driving the price of cars up."