An employer is not to discriminate against persons in hiring, retention in employment, promotions or benefits of employment because of past or present military affiliation or obligations, or because of an intent to join the military, whether it be Active, Reserve or National Guard. Uniformed service members can seek relief through the Veterans' Employment and Training Service, U.S. Department of Labor, if a conflict can't be worked out. You must serve satisfactorily or have been released from service under conditions other than dishonorable. You must not have exceeded the five-year cumulative limit on periods of service. The time limit for you to return to your civilian workplace after AT or other types of extended military leave of absence depends on the duration of the orders.
Employers also have rights.
National Guard and Reserve members are required to give their employer advance written or verbal notification of duty. Except in rare situations, employees should provide a copy of orders, the yearly drill schedule or other type of documentation for any type of military service to their civilian employer as soon as available and as far in advance as possible. Employers have the right to proof of an employee's military duty. Your employer should allow you enough time off to travel safely to drill or other military duty and arrive rested. This is administered case by case.