There are minimum pay requirements for employees who come to work for meetings or who are dismissed early from work. Many employers are either unaware of these requirements or erroneously believe that their payroll service or manager is processing such time correctly. Its called Reporting Time Pay: (See e.g. IWC Wage Order 5, #5) The rule: If an employee is relieved early from his shift, he must be paid at least half his usual or scheduled shift but not less than the amount of time he actually worked, and not less two hours nor more than four hours.
“Scheduled” vs. “usual: shift: The distinction in the rule between “usual or scheduled” shift simply recognizes that a shift can be scheduled to be a short shift. In that case, the employee only need be paid the actual shift amount as long as it is more than two hours. However, if the employee is relieved early from even the scheduled short shift, he must be paid at least half the time that was scheduled but no less than hours pay.
Meetings on off-days: When an employee reports to work on an off-day for a meeting of less than two hours duration, he or she must be paid for two hours his or her normal wage.
Exceptions: In certain circumstances, the employer need not be paid in excess of actual time worked for prematurely terminated shifts. These include events beyond the employer’s control such as bomb scares, serious weather events, or utility failures; but do not include business circumstances such as lack of customers. Additionally, employees who are terminated or sent home early for significant disciplinary reasons may not qualify for reporting time pay. The discipline exception does not include inadequate or poor performance issues.
Overtime pay vs reporting time pay: Reporting time pay is considered “premium” pay and not part of the normal time counted towards overtime. For example, if an employee works for one hour but is paid for three hours, the two additional hours would not be counted towards overtime in determining if the employee worked more than 40 hours in the week, or more than 8 hours in the day (e.g. if he/she was called back to work another shift in the same day).
How much notice? The wage order only requires reporting time pay when the employee “does report” to work. There is no explicit requirement for how long before a shift the employer must give notice that a shift is cancelled.
More detailed answers to specific factual scenarios can be found at the California Department of Industrial Standards website.