Final answer:
The Center of Nursing Advocacy is the organization that initiated a protest against the negative depiction of nurses on TV, which belongs to the wider context in which professional societies contribute to industry representation and standards.
Step-by-step explanation:
The organization that posted a call to action protesting the negative portrayals of nurses in popular television series and asked RNs to send letters of complaint to the producers of these shows is the Center of Nursing Advocacy. Professional societies like the American Hospital Association, which serves various hospitals and healthcare networks, and the National Medical Association, which has made significant contributions to the Black medical profession, often take on roles to advance the public perceptions and professional standards of their respective fields. They are not unions, but they play a crucial part in promoting networking, collaboration, and representation of industry interests, similar to the advocacy work done by the Center of Nursing Advocacy in this context.