39 U.S. Code § 1203 - Recognition of labor organizations
(a) The Postal Service shall accord exclusive recognition to a labor organization when the organization has been selected by a majority of the employees in an appropriate unit as their representative.
(b) Agreements and supplements in effect on the date of enactment of this section covering employees in the former Post Office Department shall continue to be recognized by the Postal Service until altered or amended pursuant to law.
(c) When a petition has been filed, in accordance with such regulations as may be prescribed by the National Labor Relations Board—
(1) by an employee, a group of employees, or any labor organization acting in their behalf, alleging that
(A) a substantial number of employees wish to be represented for collective bargaining by a labor organization and that the Postal Service declines to recognize such labor organization as the representative; or
(B) the labor organization which has been certified or is being currently recognized by the Postal Service as the bargaining representative is no longer a representative; or
(2) by the Postal Service, alleging that one or more labor organizations has presented to it a claim to be recognized as the representative;
the National Labor Relations Board shall investigate such petition and, if it has reasonable cause to believe that a question of representation exists, shall provide for an appropriate hearing upon due notice. Such hearing may be conducted by an officer or employee of the National Labor Relations Board, who shall not make any recommendations with respect thereto. If the National Labor Relations Board finds upon the record of such hearing that such a question of representation exists, it shall direct an election by secret ballot and shall certify the results thereof.
(d) A petition filed under subsection (c)(1) of this section shall be accompanied by a statement signed by at least 30 percent of the employees in the appropriate unit stating that they desire that an election be conducted for either of the purposes set forth in such subsection.