If you receive a letter of warning for attendance, the next step is likely an Investigation. The carrier contends this letter of warning has no expiration date and since you have been warned, improve your attendance. However, a single event of a miss call (MC) or Lay off no show (LN) have triggered investigations. The bad thing about the attendance policy is it has a 36 month retention period or 30 months if you sign a waiver. Please review the Attendance Policy.