A more thorough explanation:

Agency-shop membership is a type of union membership where a private-company employee pays the union's initiation fees and periodic dues but is not a full union member. This is also known as financial-core membership.

In states without a right-to-work law, a union-security contract clause can require employees to pay financial-core membership dues but cannot require full union membership. The dues are limited to the amount required to support the union's representational activities, such as collective bargaining.

For example, if a private-company employee in California is part of an agency-shop membership, they would pay union dues but would not have access to all the benefits and privileges of being a full union member.

Another example is a public-sector employee in New York who is part of a fair-share membership, which is the same as agency-shop membership. They would pay union dues but would not be required to participate in all union activities.