Graetz's first full-time job as pastor was to a Black congregation, Trinity Evangelical Lutheran Church, in Montgomery. He began working there in 1955, the year of the Montgomery bus boycott. A personal friend of Rosa Parks, Graetz became secretary of the Montgomery Improvement Association, the organization founded to organize and support the boycott. The Sunday after Parks was arrested and the boycott began, he told his congregation, "Let’s try to make this boycott as effective as possible because it won’t be any boycott if half of us ride the buses and half don’t ride. So if we’re going to do it, let’s make a good job of it.” Graetz's support of the movement also included appearing at meetings led by Martin Luther King Jr.