This section applies only to an employee: in the management service; in executive service; or under a special appointment described in § 6–405 of this article. An employee or an employee’s representative may file a written appeal of a disciplinary action with the head of the principal unit. An appeal: must be filed within 15 days after the employee receives notice of the disciplinary action; and may only be based on the grounds that the disciplinary action is illegal or unconstitutional. The employee has the burden of proof in an appeal under this section. The head of the principal unit may confer with the employee before making a decision. The head of the principal unit may: uphold the disciplinary action; or rescind or modify the disciplinary action and restore to the employee any lost time, compensation, status, or benefits. Within 15 days after receiving an appeal, the head of the principal unit shall issue the employee a written decision. The decision of the head of the principal unit is the final administrative decision. Within 15 days after issuance of a decision to rescind a disciplinary action, the disciplinary action shall be expunged from the employee’s personnel records.