A growing body of research has documented the uneven distribution of teacher quality across and within school districts. This paper focuses on the effect of the seniority-based transfer rules in collective bargaining agreements (CBAs) on teacher sorting. Specifically, as the seniority-preferred transfer rules in CBAs allow the more experienced teachers to transfer to more desirable positions, these rules can interfere with teacher sorting within a school district. By exploring various teachers' characteristics, this paper explores whether the transfer rules that favor seniority influence teacher mobility, resulting in an uneven distribution of the teaching workforce. Our findings show that there is no definitive answer regarding whether, across the schools, seniority rules are positively associated with less qualified teachers.