Three Arizona utilities are under investigation by federal regulators for power rates in the Tucson area.

The Federal Energy Regulatory Commission is requiring that Arizona Public Service, Tucson Electric Power Co., and UNS Electric prove they don’t have what’s known as “market power.” This could allow the utilities to manipulate or raise prices, specifically in the Tucson area.

The probe only relates to federally regulated wholesale power markets, not to any of the utilities’ residential or commercial customers.  A spokesperson for APS said the company will provide information to federal regulators within the next 60 days to comply with the order.