NEW YORK - The Federal Bureau of Investigation is reportedly looking into contracts awarded by the city's Education Department to private yellow school bus companies.

The Daily News says the bureau has subpoenaed records linked to high-ranking employees in the contracts division at the DOE's Office of Pupil Transportation.

The reason for the probe is unclear, but the Education Department tells the News it is cooperating with the investigation.

The city's yellow bus system has come under federal investigation before.

A school bus company owner and top union officials were arrested in 2008 for corruption.