The National Labor Relations Act, as amended, allows unions to require that non-union members pay agency fees to cover collective bargaining costs and prevent free rider problems.

[1][2] the Court held that the agency shop provisions of the Railway Labor Act were constitutional,[1][3] but withheld judgment as to "the validity or enforceability of a union or closed shop agreement if other conditions of union membership are imposed or if the exaction of dues, initiation fees or assessments is used as a cover for forcing ideological conformity or other action in contravention of the First or the Fifth Amendment.

"[3][4] Five years later, in Machinists v. Street, 367 U.S. 740 (1961), the Court held that the Railway Labor Act "denies the authority to a union, over the employee's objection, to spend his money for political causes which he opposes.

[1][6] Making its first private sector ruling in NLRB v. General Motors Corp., 373 U.S. 734 (1963), the Court held that agency fees equal to dues are not prohibited by the National Labor Relations Act.

[1][3][13][14] In Ellis v. Railway Clerks, 466 U.S. 435 (1984), the Supreme Court concluded that the agency fee may only cover those activities directly related to the union's role as a collective bargaining representative.

[20] In 1992, voters in the state of Washington approved a ballot initiative that requires unions to receive permission from non-union members to use their fees to support political campaigns.

[21] This included getting each person's approval even for soft money expenditures, an issue not previously covered in Supreme Court rulings.

"[24] Other legal scholars have criticized Justice Scalia's judicial reasoning in Davenport, concluding that he should have ruled solely on First Amendment grounds and overturned the agency fee law entirely.