A $125 million class action lawsuit has been filed against Hydro One over alleged improper billing and account management practices.

Koskie Minsky LLP and Lax O'Sullivan Scott Lisus LLP filed the suit against Hydro One, as well as four of its subsidiaries, on Wednesday at the Ontario Superior Court of Justice.

The law firms say the claim is being brought on behalf of all Hydro One customers who have used the service since May of 2013. Hydro One customer Paul Foster is set to be the representative plaintiff in the case.

Ontario's Ombudsman Andre Marin blasted Hydro One in a May report that found some 100,000 households had massive billing errors, which were attributed to a new billing system. Marin said his office received more than 10,000 complaints from Hydro One customers about over-billing.

The class action lawsuit focuses on the problems surrounding the rollout of the new billing system. The lawsuit alleges:

Thousands of customers stopped receiving bills.

Others received bills based on estimates, then later received "massive 'catch-up' bills."

Hydro One automatically withdrew large quantities of money from customers' accounts without notice or explanation.

Thousands of customers dealt with billing and administrative errors, including "bills that did not reflect the electricity actually consumed."

"Hydro One customers are particularly vulnerable to Hydro One's administration and billing abuses as a result of its near monopolistic nature and the importance of the services it renders to customers," said Kirk M. Baert, a partner at Koskie Minsky LLP, in a news release about the court filing.

Eric R. Hoaken, a partner at Lax O'Sullivan Scott Lisus LLP said, in the same release, "It's time that Hydro One accounted for the billing abuses it has perpetrated on its customers."

In the wake of the ombudsman's report, Hydro One officials said the utility has fixed its billing issues and said the company is working to improve its customer service.