He joined the United Association union, and served as business manager of his local union for many years. In 1988, he was elected as a vice president of the union, then became a full-time international representative, before in 1996 winning election as the union's general president.[1][2][3]
As leader of the union, Maddaloni focused on organizing more members, and maintaining high quality training programs.[2] Maddaloni also served as a vice-president of the AFL-CIO from 1995.[1]
In 2004, Maddaloni and the union's secretary-treasurer Thomas H. Patchel were accused of mismanaging the union's finances. In particular, their decision to invest pension funds in a Florida hotel was questioned. The United States Department of Labor required them and two other trustees to resign from the union's pension fund, and pay $11 million in penalties. The union then bought both Maddaloni and Patchel out of their contracts, with the two resigning their posts, and in 2005 resigning from the union entirely.[4][5]