Proposed rules that would subject large debt collectors and credit reporting agencies to Consumer Financial Protection Bureau supervision are likely to be controversial because they include law firms, Ballard Spahr partner Christopher J. Willis said.

"Firms may argue they're regulated in other ways, by the rules of court and ethical obligations, and [CFPB oversight] is not necessary," Mr. Willis said. He added that law firms may be collecting debts on behalf of entities such as mortgage servicers that are already under CFPB supervision.