"The OPP is conducting an investigation into possible criminal activities on the part of Ornge air ambulance service," police spokeswoman Cathy Bell said Thursday.
The investigation was launched at the request of the Ministry of Health and Long-Term Care, she added.
Sources said the ministry asked police to look into "financial irregularities" at Ornge after receiving advice from forensic auditors who examined its books.
The criminal investigation is the latest blow to Ornge, which receives about $150 million a year from the province to operate a non-profit air medical rescue and transport service.
The publicly funded agency, which set up a series of private for-profit entities, has been under fire for months over questionable business dealings and exorbitant executive salaries.
Police, Ornge and Health Minister Deb Matthews declined to say what prompted the investigation, but the minister said she's disappointed that the police had to be called in.