The union that serves doormen, porters and other building employees is falling into the Gap — or at least where the retailer used to have offices.

The Service Employees International Union Local 32BJ signed a 20-year deal to move into more than 283,000 square feet at 620 Avenue of the Americas, a building owned by the Chetrit family, Yair Levy and Bonjour Capital. The space on the fourth through seventh floors was previously occupied by Gap.