A petition may be filed with the board, in accordance with its rules and regulations, requesting it to investigate and decide the question of whether employees have selected or wish to select an exclusive representative or to determine the appropriateness of a unit, by:
(a)
An employee organization alleging that it has filed a request for recognition as an exclusive representative with an employer and that the request has been denied or has not been acted upon within 30 days after the filing of the request; or
(b)
An employee organization alleging that it has filed a competing claim of representation pursuant to subdivision (b) of Section 3574; or
(c)
An employee organization wishing to be certified by the board as the exclusive representative. Such petition for certification as the exclusive representative in an appropriate unit shall include proof of a 30-percent showing of interest designating the organization as the exclusive representative of the employees.