ByJohn S. McClenahen The number of mass layoffs in U.S. manufacturing, those affecting at least 50 workers in a single facility, rose last month, according to data released May 26 by the U.S. Department of Labor's Bureau of Labor Statistics. During April there were 343 mass layoffs among U.S. manufactures, up from 258 in March and 240 in February. April's layoffs affected 36,172 workers, up from 34,686 in March and 23,043 in February, with food-processing and auto workers accounting for the largest shares.