Using mathematics as a tool to interrogate (in)justice and take action toward a more socially just world in PreK-12 mathematics shows promise for disrupting marginalization of Black and Brown students. Teachers, however, work within broader systems, structures, and discourses that shape their decisions and actions. Consequently, they likely feel imbalance, and attempts to manage tensions may inadvertently perpetuate whiteness -- the ideologies that value the white racial group over others. To explore this phenomenon, we asked: How do white teachers learning to teach mathematics for social justice disrupt whiteness in mathematics education, and how do they perpetuate whiteness? We examined two newly practicing teachers' social justice mathematics lesson planning, enactment, and reflection through a framework for the operation of whiteness in mathematics education. Findings provide insights into the perpetuation and disruption of whiteness in the institutional and labor dimensions of mathematics teaching and learning as teachers sought to balance mathematics and social justice goals and connect to Black and Brown students' experiences. We discuss implications for the continued learning of social justice teaching and the development of resources to support disruption of whiteness in mathematics education.