TORONTO -- Four Mississauga residents are facing charges following an investigation into fraud allegations connected to contracts involving Hydro One.

Provincial police say information provided by the Ontario Crown corporation's internal security team alleged that a former contract employee of a company responsible for obtaining materials and equipment manipulated bids to award contracts to family members or friends. They say the contracts involved materials such as fuses, cable, steel and machinery supplies.

Police say they believe the former contract employee received payments from one or more of the successful vendors and more than $500,000 worth of contracts had been unfairly awarded between November 2010 and February 2013.

Police say two women, Tanveer Nazriddin, 40, Zainab Noman, 37, and one man, Muhammad Yusuf, 40, have been charged with fraud over $5,000, bribery of an agent and laundering the proceeds of crime. Another man, Naziruddin Syed, 46, also faces charges of fraud, bribery and possession of the proceeds of crime.

A spokesman for Hydro One says the corporation has been cooperating with OPP in the investigation, adding it takes the matter extremely seriously.

Police say the probe is ongoing and more information will be released during a news conference in Hamilton on Friday. All four accused are expected to appear in court in Toronto on May 19.