In California, employers generally can make employees work whenever employers want for as long as employers want with or without providing advanced notice to employees. However, employers must comply with applicable overtime pay, meal period, and rest period rules required by the law.
For example, an employee may be scheduled to work from 10:00 a.m. to 6:00 p.m. on a Monday. An employer in this example has the right to call the employee at 11:30pm on the night before (Sunday) and tell the employee to come to work at 5:00 a.m. the next morning and still work to 6:00 p.m. Monday. Forcing an employee to start work five (5) hours earlier and work a shift totaling thirteen (13) hours on short notice instead of a scheduled eight (8) hour shift sounds pretty ridiculous and unfair but it does not violate the law and employees do not have the right to be free from working conditions like these.
The practical realties are that employers tend to stick to work schedules and avoid overworking employees because employees, particularly if they are at-will employees, can just quit on the spot without giving the employer notice when employees do not like the working conditions.One narrow exception is that that employers cannot fire or discipline an employee for refusing to work more than 72 hours in a workweek unless the employer has an unavoidable or unpredictable emergency requiring immediate action, or the employee has been properly classified as administrative, executive, or professional exempt.
(See Link(s): Industrial Welfare Commission Wage Orders)