This study aims to explore whether teachers' voice behavior is triggered by the leadership of the principal or the teachers themselves. Two conceptual frameworks are proposed to guide this research. In addition, the current study analyzes separately two dimensions of teachers' voice behavior, namely, promotive voice and prohibitive voice. Data collected from 884 teachers in Taiwan were analyzed to test the moderated mediation model. Results of the first conceptual framework revealed that under identity leadership, teacher agency moderated significantly the relationship of psychological empowerment with prohibitive voice, but not significantly with promotive voice. Findings of the second conceptual framework confirmed that under teacher agency, identity leadership did not significantly moderate the relationships of psychological empowerment with promotive voice and prohibitive voice. Most important, this study discovered that teacher agency is the main trigger for teachers exhibiting promotive and prohibitive voice behaviors. Finally, implications and limitations of this study are presented.