All personnel employed by the department of health and human services, the regional offices of that department, job service North Dakota, North Dakota human resource management services, department of environmental quality, and other agencies or political subdivisions as may by federal law or rule be required to be subject to a merit system in order to obtain federal grants-in-aid are covered by the merit system provided in this chapter. Merit system coverage must also be provided to personnel employed as purchasing agents or buyers in the purchasing division of the office of management and budget. Other agencies, departments, or divisions and positions must be placed under a merit system in the manner and to the extent required by law.