A National Labor Relations Board judge ruled on Tuesday that Starbucks had illegally fired three baristas and otherwise violated federal labor laws in seeking to beat back unionization efforts at several of its Manhattan cafes. The administrative law judge, Mindy E. Landow, found that Starbucks had also broken the law by issuing negative job evaluations to union supporters and prohibiting employees from discussing the union even though the employees were allowed to discuss other subjects not related to work.