Utility profit margins are capped by state regulation. Ameren Missouri currently is allowed up to a 10.2 percent return on equity and had sought to increase that to 10.5 percent. Instead, the PSC capped that at 9.8 percent, which it said was a little below the average rate allowed nationally.
Decreasing the amount of money Ameren can earn could make it more difficult for the company to attract the investors, Wood said.
But commissioner Robert Kenney, who cast the lone no vote, said the earnings percentage was too high considering Ameren already is able to quickly recover its fuel costs and recoup money spent on repairing storm damage and clearing trees away from power lines.
"The commission has made it easier, faster and less risky for Ameren to collect its money from its customers," Kenney said.
John Coffman, an attorney for the Consumers Council of Missouri and AARP Missouri, said his clients advocated for an 8 percent return on equity for Ameren.
The amount approved by regulators is "out of sync with the very, very low interest rates and economic conditions that we're currently experiencing," Coffman said.
But Coffman was complimentary of at least one portion of Wednesday's decision. He praised regulators for rejecting Ameren's request to increase the fixed cost on residents' monthly bills to $12 from the current $8.
Combining Wednesday's rate hike with others from the past six years, utility regulators now have allowed Ameren to increase its revenues by nearly $1 billion, said Chris Roepe, executive director of the Fair Energy Rate Action Fund, which represents consumers and industrial energy users.
"These actions absolutely undermine what was not too long ago a strength in Missouri — low energy costs," Roepe said.
Wood said Ameren's rates will remain below national and regional averages, even with the latest increase.