The military says Hynes has been relieved due to loss of confidence in his ability to command.
The Army has not said what Hynes is accused of doing.
Lt. Col. Albert Paquin will temporarily take command of the 2nd Brigade Combat Team.
Prior to the investigation, the Army had already chosen Col. Joseph Ryan to succeed Hynes as the brigade commander. Ryan is scheduled to take command of the 2nd Brigade Combat Team in July.