There are no federal laws that require employers to provide employees time off to vote.  California has laws that require private employers to give employees time off to vote, and, in some cases, the employee must be paid for this time.

California law states:

If an employee does not have sufficient time outside of working hours to vote, the employer must provide enough time off that, when added to time available outside of working hours, the employee will be able to vote.  Unless otherwise agreed, the time off must be at the beginning or end of a shift, whichever allows the most free time to vote and the least time off from work.  Employees who, three working days before the election, have reason to believe that time off will be necessary must give the employer two business days’ notice. Up to two hours off must be paid. Employers must post, in a conspicuous place, a notice setting forth these provisions no less than 10 days before the election.