The MBTA is investigating after discovering discrepancies between how many cars were parking in some of its contractor-managed lots and how much money was being collected.

The Massachusetts Bay Transportation Authority is focusing on three lots managed by LAZ Parking at the North Quincy/Hancock, Lechmere, and Riverside stations.

If the T is able to document money is missing, LAZ would have to repay the T double the amount, plus fines.

Officials have not said how much money they suspect is missing or whether a criminal investigation is underway.

A T lawyer says LAZ was alerted to the discrepancy in April and has fired two employees for not following proper procedures. LAZ says its own investigation found no revenue loss at Riverside.