Union dues are the regular payments members make to support the organization’s administrative costs. Editors Guild members pay dues on a quarterly basis and on a sliding scale; those working in higher-paid classifications pay more than those working in lower-paid classifications. Picture editors, for example, usually pay about $300 per quarter (depending upon the contract under which they work), while loggers pay $120.
More detail about how members' dues are calculated is available here.
Unlike other forms of representation that you can purchase -- by hiring an agent or hiring a lawyer to represent you, for example -- union representation does not operate on a fee-for-service model. Although dues are necessary to fund the organization’s staff, facilities, and projects, members are not simply hiring the union to act on their behalf.
The strength that we have derives not from the monies members pay, but instead from the solidarity members show. When the Guild negotiates a strong contract for a group of employees, the strength of that contract chiefly comes not from the expertise of a professional negotiator -- although the Guild does indeed employ experienced and talented negotiators on its staff -- but instead from the leverage the crew generates through its cohesion and commitment. Dues keep the lights on, but it’s solidarity that powers the union.