CBI sources said the agency got a tip-off about the alleged scam from a whistleblower.
The sources said all the appointments done in the force during last two years are under the CBI scanner but so far no PE or case has been registered by it.
This comes close on the heels of the bribery scam involving Vijay Singla, nephew of Railway Minister Pawan Bansal and Railway Board member Mahesh Kumar.