(1) It shall be presumptively appropriate to include regular part-time employees in the same bargaining unit with full-time employees performing similar work, in order to avoid a potential for conflicting work jurisdiction claims which would otherwise exist in separate units. Employees who, during the previous twelve months, have worked more than one-sixth of the time normally worked by full-time employees, and who remain available for work on the same basis, shall be presumed to be regular part-time employees. For employees of school districts and educational institutions, the term "time normally worked by full-time employees" shall be based on the number of days in the normal academic year.

(2) It shall be presumptively appropriate to exclude casual and temporary employees from bargaining units.

(a) Casual employees who have not worked a sufficient amount of time to qualify as regular part-time employees are presumed to have had a series of separate and terminated employment relationships, so that they lack an expectation of continued employment and a community of interest with full-time and regular part-time employees.

(b) Temporary employees who have not worked a sufficient amount of time to qualify as regular part-time employees are presumed to lack an expectation of continued employment and a community of interest with full-time and regular part-time employees.

(3) The presumptions set forth in this section shall be subject to modification by adjudication.