The Consumer Financial Protection Bureau’s lawsuit to claw back millions of dollars in debts collected by Frederick Hanna’s Marietta law firm is a particularly challenging test case for the fledgling federal agency.

The agency has targeted Frederick J. Hanna & Associates as a “lawsuit mill,” claiming it uses illegal tactics to intimidate consumers into paying debts they do not owe. But Hanna already has beaten back similar claims in both state and federal courts in Georgia.