SEC officials signaled this week that the agency is revisiting the rules regarding annual 12b-1 fees in mutual funds.

The fees — generally between 0.25 percent and 1 percent (the maximum allowed) of a fund's net assets – are part of the conflict-of-interest debate that has motivated the universal fiduciary rule in the works at the Department of Labor. 

The fees are covered by investors' assets and pay for distribution, including expenses related to marketing to brokers as well as their compensation. The fees also cover the cost of delivering fund prospectuses to investors and the cost of sales literature. In some cases, 12b-1 fees also cover the cost of shareholder services, like call centers that field investors' inquires.