A business league exempt under Code section 501(c)(6) organization is a membership organization characteristically supported by dues. Although an organization may receive a substantial portion or even the primary part of its income from non-member sources, membership support, either in the form of dues paid to or involvement in the organization's activities, must be meaningful.
For this purpose, membership support includes the following items:
Amounts derived from performing the organization's exempt functions or from substantially related activities
Contributions or gifts from the general public
Unrelated income is excluded in measuring the extent of membership support. Thus, for example, dues from associate members are generally not considered.