PHOENIX — A highly-anticipated hearing began Tuesday at the Arizona Corporation Commission that is meant to determine whether a rate hike approved for APS customers last year is unjust, or at the very least has resulted in “unintended consequences,” as one commission staff member explained.

An administrative law judge is overseeing the hearing, expected to last through at least Wednesday. The judge will provide a recommendation to the commission after reviewing testimony.

Last year the corporation commission approved a complex rate agreement that allows for APS to collect 4.54 percent more revenue from customers compared to a 2015 baseline year. More than two dozen parties were involved in the hearings, including representatives of low-income customers.

During Tuesday’s morning session, utility consultant Abhay Padgaonkar, who represents customers filing the complaint, testified that he has analyzed thousands of APS customers’ bills revealing an average percentage rate increase that is two to three times the amount approved.

However, an attorney for APS told the commission there is “an erroneous contention that APS is collecting more revenue than was authorized and is over-earning.”

“Simply running rates though a model doesn't properly account for all of the intricate and interdependent aspects of rate-making customer benefits that all work together to establish the reasonableness of APS’s rates,” said attorney Melissa Krueger.

It was earlier this year when APS customer and renewable energy advocate Stacey Champion filed a petition that prompted the hearing to take place. Champion is running a Go Fund Me legal fund that has raised more than $20,000 to pay for the legal challenge. According to Champion, she has already exhausted those donations and is paying out of her own pocket.

“I probably didn't really understand the magnitude of how large this project would be, going up against a multi-billion dollar utility monopoly. Yet here we are," Champion said.

During a public comment session Tuesday, APS customers told the commission they didn't trust the utility company. They told stories about unusually high bills and negative experiences dealing with APS customer service representatives. Several low-income customers explained hardships they have experienced because of increased APS bills. One customer complained that she believes the elected commissioners have become too friendly with the utility.

APS maintains it is abiding by the settlement agreement and says one customer’s experience does not reflect the overall picture. The company provides energy-use options to help customers to save money and financial help for low-income customers, a spokesperson said.