concurring.
I concur with the result the majority reaches, but my reasons are different. In my view, the National Labor Relations Board’s (Board’s) construction of section 1205 of the Postal Reorganization Act (Postal Act), 39 U.S.C. § 1205, cannot withstand scrutiny. I would hold that the statute precludes the Postal Service’s giving effect to Dalton’s revocation.
Although we accord deference to the interpretation the Board gives to statutes involving labor-management relations, International Alliance of Theatrical Stage Employees v. NLRB, 779 F.2d 552, 555 (9th Cir.1985), cert. denied, — U.S.-, 106 S.Ct. 3273, 91 L.Ed.2d 563 (1986), the courts are the final authority on statutory construction. See SEC v. Sloan, 436 U.S. 103, 117-18, 98 S.Ct. 1702, 1711, 56 L.Ed.2d 148 (1978) (citations omitted). Section 1205 authorizes the Postal Service, upon the agreement of an employee and the Postal Service, to deduct union membership dues automatically from the employee’s paycheck. If the employee makes such an agreement, it “shall be irrevocable for a period of not more than one year.” 39 U.S.C. § 1205. The Board asserts that because section 1205 is similar to section 302(c) of the National Labor Relations Act (NLRA), 29 U.S.C. § 186(c), case law under the NLRA controls the irrevocability of an authorization under section 1205. I disagree.
First, the difference in language1 between section 1205 and section 302(c) is more than minor. Section 302(c) is permissive: it states that an authorization “shall not be irrevocable for a period of more than one year.” The provision does not require an authorization to be irrevocable; *556it merely puts a time limit on the authorization if the parties agree to make it irrevocable. Section 1205, on the other hand, expressly requires irrevocability, although it leaves the time period to the discretion of the parties to the authorization.
The majority argues that despite the “ambiguous” language of section 1205, which it concedes might prevent revocability in typical circumstances, an exception to irrevocability should be made where an employee resigns his or her membership from the union. Under the NLRA, “as a matter of law” the authorization is revoked under these circumstances if dues are a “quid pro quo” for union membership despite an irrevocability clause in the agreement. It is a violation of section 8(b)(1)(A) to continue to withhold dues. San Diego County District Counsel of Carpenters, 243 N.L.R.B. 147, 149 (1979) (Campbell); see also Steelworkers, Local 7450, 246 N.L.R.B. 878, 882 (1979) (Asarco, Inc.).
These cases, in my view, do not control interpretation of the Postal Act. The Postal Act adopts the NLRA only insofar as no provisions of the NLRA conflict with the provisions of the Postal Act. 39 U.S.C. § 1209(a). In this case, even if we were to apply the NLRA to provisions of the Postal Act, we would have to overcome the express Congressional mandate of section 1205.2
Support for the position that the Postal Service may continue to withhold dues even though an employee resigns from his or her union is furnished by the historical context in which section 1205 was passed. Before the Postal Act, labor relations in the Postal Service were governed by two Executive Orders generally applicable to the federal sector: Exec. Order No. 10,998, 27 Fed.Reg. 551 (1962) and Exec. Order No.
11,491, 34 Fed.Reg. 17,605 (1969). Exec. Order No. 11,491, § 21 provides that an employee may sign check-off authorizations “which shall include provision for the employee to revoke his authorization at stated six-month intervals.” The authorization terminates when
(1) the dues withholding agreement between the agency and the labor organization is terminated or ceases to be applicable to the employee; or
(2) the employee has been suspended or expelled from the labor organization.
34 Fed.Reg. at 17,614.
That the Executive Order did not include membership resignations, but did include the similar circumstances of suspension or expulsion, would indicate that a resignation was not grounds for termination. The Federal Labor Relations Authority recently construed 5 U.S.C. § 7115, which essentially 3 codified this section of Exec. Order No. 11.491, and held that an employee who resigned from his union because he switched trades within his job and joined another more applicable union was unable to revoke his authorization. Portsmouth Naval Shipyard, 19 F.L.R.A. No. 77 (Aug. 12, 1985).
The purposes of authorizing the irrevocable check-off agreements would be undermined if we were to make an exception in this case. By authorizing irrevocability, section 1205 decreases record-keeping for the Postal Service. Irrevocability also enables a union to plan its finances with greater accuracy. The fact that a union member decides to withdraw from the union does not diminish the force of these policies.
I conclude that section 1205 requires that the check-off agreement be irrevocable *557even when a member resigns his or her membership.4 Accordingly, I concur.
. The meaning of a statute is derived first from its language. Unless legislative intent is clearly contrary to the statutory language, the language is ordinarily considered conclusive. Consumer Prod. Safety Comm'n v. GTE Sylvania, 447 U.S. 102, 108, 100 S.Ct. 2051, 2056, 64 L.Ed.2d 766 (1980).
The legislative history concerning section 1205 is slight. The parties refer the court to a conversation between then-Congressman Gerald Ford and Congressman William Ford. Their discussion supports the statutory language to the extent that they consider the authorizations irrevocable, but the Congressmen did not address the precise question of whether resignation from a union is an exception to the general rule.
. The Board argues also that irrevocability is at least a partial restriction upon an employee’s right to resign from union membership and that restrictions on the right to resign violate the NLRA. I do not consider this argument because it was not a basis of the Board’s decision. A Court of Appeals may not permit the Board’s General Counsel to substitute a post hoc rationale for the Board’s own reasoning. NLRB v. Metropolitan Life Insur. Co., 380 U.S. 438, 442-44, 85 S.Ct. 1061, 1063-64, 13 L.Ed.2d 951 (1965); SEC v. Chenery Corp., 332 U.S. 194, 196, 67 S.Ct. 1575, 1577, 91 L.Ed. 1995 (1947).
. Read in context, the words "member” and "dues" simply refer to the employee’s status at the time of authorization and to the purpose for which the employee authorized the withholding of funds.
. Section 7115 changed the language from the authorization "terminates" to the authorization "may not be revoked for a period of one year.” Because Congress was considering "termination” in passing section 1205, it is conceivable that Executive Order 11,491 does not speak to whether a resignation was grounds for revocation. At a minimum, however, the order indicates that Congress was aware that circumstances arose in which employees left their unions, and did not alter its mandatory language.