An Amazon.com Inc. unit violated federal labor when it interrogated employees about their unionization efforts and fired an employee during an organizing campaign at a San Francisco facility, a National Labor Relations Board judge ruled.

Administrative Law Judge Michael P. Silverstein ordered Amazon.com Services LLC in on Friday to reinstate and issue back pay to a former employee who was terminated for his union activities. The opinion also ordered Amazon to reinstate another employee to a learning ambassador program that the judge found she was excluded from due to her organizing activities.

The ruling is the latest in a series …