1) Employers can set the terms and conditions of employment, including what tasks employees do. Regardless of your job title or description, your boss can ask you to do other tasks. For example, even managers could be made to do janitorial tasks.2) Employers set the hours and days of employment; an employer can require someone to work on weekends, evenings, etc.3) If you were overpaid for the amount of work you actually did (i.e. you are an hourly employee, and you were paid for more hours than you worked), the employer can require you to return the money; alternately, you and he can work out some other way to pay it back, such as by working enough extra hours to "use up" the overpayment.4) However, employers may not avoid overtime requirements. Under federal law, if you are a nonexempt employee, you must be paid time and half for all hours over 40 worked in one work week. Under CA law, you need to be paid overtime (time and a half) for all hours over 8 worked in one work day.