(a) Representatives designated or selected for the purposes of collective bargaining by the majority of the employes in a unit appropriate for such purposes, shall be the exclusive representatives of all the employes in such unit for the purposes of collective bargaining in respect to rates of pay, wages, hours of employment, or other conditions of employment: Provided, That any individual employe or a group of employes shall have the right at any time to present grievances to their employer.

(b) The board shall decide in each case whether, in order to insure to employes the full benefit of their right to self-organization and to collective bargaining, and otherwise to effectuate the policies of this act, the unit appropriate for the purposes of collective bargaining shall be the employer unit, craft unit, plant unit, or subdivision thereof: Provided, That if the majority of the employes of a particular craft signify a wish for a craft unit, the board shall designate the craft unit as the unit appropriate for collective bargaining for the employes of that particular craft.

(c) Whenever a question arises concerning the representation of employes the board may, and, upon request of a labor organization, or an employer who has not committed an act herein defined as unfair labor practice, or any group of employes in an appropriate unit representing by petition thirty per centum or more of the employes of that unit, shall investigate such controversy and certify to the parties, in writing, the name or names of the representatives who have been designated or selected. In any such investigation, the board shall provide for an appropriate hearing upon due notice, either in conjunction with a proceeding under section eight,¹ or otherwise, and may utilize any suitable method to ascertain such representatives, except that if either party to the controversy so requests, a secret ballot of employes shall be taken within twenty days after such request is filed. Any certification of representatives by the board shall be binding for a period of one year, or for a longer period if the contract so provides, even though the unit may have changed its labor organization membership.

(d) Whenever an order of the board, made pursuant to section eight, subsection (c), is based, in whole or in part, upon facts certified following an investigation pursuant to subsection (c) of this section, and there is a petition for the enforcement or review of such order, such certification and the record of such investigation shall be included in the transcript of the entire record required to be filed under subsections (a) or (b) of section nine,² and thereupon the decree of the court enforcing, modifying or setting aside, in whole or in part, the order of the board, shall be made and entered upon the pleadings, testimony, and proceedings set forth in such transcript.