Duke Energy Florida will have to explain to state regulators an ongoing change in its billing process that two lawmakers say is spiking costs.

Public Service Commission Chairman Art Graham on Aug. 25 asked Alex Glenn, president of Duke Energy Florida, to appear at a Sept. 4 meeting to address concerns raised by state Sens. Jack Latvala, R-Clearwater, and Jeff Brandes, R-St. Petersburg, about billing-cycle adjustments and related increased customer payments.