(a) Unless modified by union contract, an employer may dismiss any employee:
(1) who engages in a business which conflicts with his duties to his employer or renders him a rival of his employer;
(2) whose insolent or offensive conduct toward a customer of the employer injures the employer's business;
(3) whose use of intoxicants or controlled substances interferes with the proper discharge of his duties;
(4) who wilfully and intentionally disobeys reasonable and lawful rules, orders, and instructions of the employer; provided, however, the employer shall not bar an employee from patronizing the employer's business after the employee's working hours are completed;
(5) who performs his work assignments in a negligent manner;
(6) whose continuous absences from his place of employment affect the interests of his employer;
(7) who is incompetent or inefficient, thereby impairing his usefulness to his employer;
(8) who is dishonest; or
(9) whose conduct is such that it leads to the refusal, reluctance or inability of other employees to work with him.
(b) The Commissioner may by rule or regulation adopt additional grounds for discharge of an employee not inconsistent with the provisions enumerated in subsection (a) of this section.
(c) Any employee discharged for reasons other than those stated in subsection (a) of this section shall be considered to have been wrongfully discharged; however, nothing in this section shall be construed as prohibiting an employer from terminating an employee as a result of the cessation of business operations or as a result of a general cutback in the work force due to economic hardship, or as a result of the employee's participation in concerted activity that is not protected by this title.