The Labor Department’s new associate deputy secretary is a prominent management attorney known for arguing against unions and worker-friendly decisions by the National Labor Relations Board.

Michael Avakian recently drew attention for his defense of a company trying to overturn the board’s decision expanding the definition of a joint employer for unionization purposes. He now reports to Deputy Labor Secretary Patrick Pizzella, Avakian’s firm announced.

Avakian was practicing management-side firm Wimberly & Lawso, when he was tapped for the job. The firm wrote in a statement that in his new role, Avakian “will be at the center of the Department’s...