Is it legal, in Iowa, to require workers to work off the clock?

If you are an hourly employee, then every state law requires that you be paid for each hour you are actually working.  An employer cannot force you to work "off the clock" without violating the law if the employer fails to pay you the proper hourly rate for the actual time you worked.  An employer sometimes asks employees to work off the clock to avoid paying overtime.  This is also a violation since it deprives you of earning overtime pay.  You should speak to an attorney to investigate this further.