Two union leaders and longtime Democratic National Committee members have resigned from the national party, marking the latest internal dispute of chairman Ken Martin’s tenure.

The Democratic Party faces new turmoil as top labor union presidents exit DNC, citing concerns about party leadership direction in a resignation letter to Chair Ken Martin.

Randi Weingarten, head of one of the nation’s most influential teachers unions, and Lee Saunders, the president of a large union of public workers, each pointed to Ken Martin’s leadership.