S.D. Codified Laws § 3-18-5
When a question concerning the representative of employees is raised by the governmental agency, labor or employee organization, or employees, the Department of Labor and Regulation or any person designated by it shall, at the request of any of the parties, investigate such question and certify to the parties in writing, the name or names of the representatives that have been designated or selected. The filing of a petition for the investigation or certification of a representative of employees by any of the parties shall constitute a question within the meaning of this section. In any such investigation, the department may provide for an appropriate hearing, and shall take a secret ballot of employees to ascertain such representatives for the purposes of formal recognition. If the department has certified a formally recognized representative in a unit of employees as provided in § 3-18-4, it shall not be required to consider the matter again for a period of one year unless it appears to it that sufficient reason exists.
SDCL 3-18-5