When an application is signed by an agent claiming to represent a majority of such employees the commissioner shall, before proceeding further, satisfy himself by secret ballot or otherwise that such agent is duly authorized to represent a majority of such employees. If the commissioner requires such secret ballot all regular employees of the unit may vote thereat. If the commissioner does not require a secret ballot he shall require a statement in writing from a majority of the employees that said agent is duly authorized to represent them. In the latter case the names of the employees giving written authority to such agent shall be kept secret by the commissioner.