Although it is one of the smaller unions in the AFL-CIO (a federation of 56 unions in the United States), like the vast majority of its fellow unions, the International Association of Fire Fighters survives on the dues and fees it collects from union members.
How much the IAFF takes in from its members through their local unions, as well as where the union spends money is public information and can be found through the U.S. Department of Labor (here).
In 2018, the IAFF took in over $48.7 million from "per capita taxes" (the per member charge a union charges its union locals), as well as an additional $275,000 "fees, fines, assessments and work assessments." In addition to loans and other revenues, the union brought in over $74.3 million in 2018.
Yet, the union spent over $75 million.
Here's the breakdown, according to the financial reports on file with the U.S. Department of Labor:
Like other unions in the AFL-CIO, the IAFF depends on union dues and fees to pay its officers and staff in its Washington D.C., headquarters. According to data the IAFF files with the U.S. Department of Labor, dozens upon dozens of union officers rake in six-figure salaries.