49 CFR 391.23
(a) Except as provided in Subpart G of this part, each motor carrier shall make the following investigations and inquiries with respect to each driver it employs, other than a person who has been a regularly employed driver of the motor carrier for a continuous period which began before January 1, 1971:
(a)(1) An inquiry into the driver's driving record during the preceding 3 years to the appropriate agency of every State in which the driver held a motor vehicle operator's license or permit during those 3 years; and
(b) The inquiry to State agencies required by paragraph (a)(1) of this section must be made within 30 days of the date the driver's employment begins and shall be made in the form and manner those agencies prescribe. A copy of the response by each State agency, showing the driver's driving record or certifying that no driving record exists for that driver, shall be retained in the carrier's files as part of the driver's qualification file.
(c) The investigation of the driver's employment record required by paragraph (a)(2) of this section must be made within 30 days of the date his/her employment begins. The investigation may consist of personal interviews, telephone interviews, letters, or any other method of obtaining information that the carrier deems appropriate. Each motor carrier must make a written record with respect to each past employer who was contacted. The record must include the past employer's name and address, the date he/she was contacted, and his/her comments with respect to the driver. The record shall be retained in the motor carrier's files as part of the driver's qualification file.
[35 FR 6460, Apr. 22, 1970, as amended at 35 FR 17420, Nov. 13, 1970].