It’s no secret that associations lose revenue each year when room blocks at hotels go unfilled. But just how much are they losing? And who else takes a financial hit?

ABTS Convention Services aimed to answer those questions in a survey of the 20 medical associations it serves. The bottom line? Those groups lose about $50 million annually because of “around the block” booking. And the cities that host the meetings could see losses of about $12 million as a result of fewer attendees, ABTS said.

Those findings were enough to prompt the group to launch an awareness campaign—“Support Associations, Book Official Housing”—designed to help associations explain to their attendees the effects of the practice on the association and on attendees’ meeting experience.

“When attendees stay outside the official housing hotels, they do not have access to room drops, announcements, free shuttles, free or reduced meals, networking events, and other happenings that are a big part of the annual meeting experience,” ABTS President Davide Veglia said in a statement. “These attendees often end up paying more in fees and transportation and [are] disappointed overall with the experience.”

Associations may face attrition penalties when pre-contracted rooms go unused, Veglia noted. Also, “guaranteeing room blocks gives associations the opportunity to negotiate concessions,” he said. “‘Around the block’ booking decreases the association’s negotiating power—ultimately making the meeting more expensive and more complicated.” That can translate into fewer attendees, draining revenue from the hotels, restaurants, and the host city as well as the association, according to ABTS.

The campaign website features a “revenue loss calculator” that allows meeting professionals to estimate how around-the-block booking would impact their own events. (ABTS also launched a free app on Google Play and in Apple’s App Store.)

“Through industry support and unification, as well as the right tool for international planners, we can steer the movement back in favor of associations,” Veglia said.

How does your association keep attendees in the official room block? Share your tips—or concerns—in the comments.