Unions seek to protect and promote the mutual interests of workers through collective bargaining. They perform both militant functions like negotiating wages and job security, as well as fraternal functions providing financial and medical assistance to workers. Unions also engage in political activities by affiliating with political parties and social service activities. They can take on various roles from advocating for worker interests to considering the interests of the organization or acting as agents of change. Unions can be based on ideology, trade or type of agreement between workers and employers.