The Diocese of San Fernando de La Union (Latin: Dioecesis Ferdinandopolitana ab Unione) is a Latin Church ecclesiastical territory or diocese of the Catholic Church in the Philippines.

The diocese was established in 1970 from the Archdiocese of Nueva Segovia.

[2] It is a suffragan in the ecclesiastical province of the metropolitan Archdiocese of Lingayen-Dagupan.