It is possible for strip club dancers in the United States to form a topless union. This could be done by forming an organization or association for those working in topless entertainment.
This organization could negotiate with strip clubs and other topless venues on behalf of its members. It could also provide support and resources to topless dancers, such as legal advice, counseling, and other services.
This organization would also need to be affiliated with a larger union, such as the Service Employees International Union, in order to gain recognition and leverage for its members.