Forest Wakefield, who runs the Log Cabin Motel in Pinedale with his wife, said the change has resulted in their motel's power bill going up two to three times what it was last year.
The Wakefields said they're worried this winter's electric bills will force them to close the motel until spring.
The billing change assesses additional fees on certain customers with higher power demands.
About 6,500 of Rocky Mountain Power's nearly 130,000 customers in Wyoming were affected by the new formula, according to Chris Petrie, secretary and chief counsel for the Wyoming Public Service Commission.
Rocky Mountain Power spokesman David Eskelsen said the change was needed to help pay for millions of dollars in new power generators and infrastructure.
Eskelsen acknowledged that some Wyoming power customers have seen "dramatic" changes in their power bills, but he said Rocky Mountain Power is working to help them find ways to lower their electricity usage.
In the Wakefields' case, conducting an energy audit might help the couple find ways to lower their energy usage, Petrie said.
But Wakefield said that's not practical for a motel.
"If you're running a hotel, you should tell your clients to not take a shower or use the water heater?" Wakefield said.