The MIA surveyed 1,180 venues and 58% of respondents said public sector clients had cancelled event bookings in the past two weeks.
Almost half of the venues that did not report cancellations said they had been warned by government clients to expect a reduced level of business.
More than a third of respondents reported that public sector clients had renegotiated confirmed and agreed rates over the period.
MIA chairman Peter Darnell said: "This is a worrying although not wholly unexpected picture for our members and the industry, and we will be doing everything possible to offer as much support as we can over the coming weeks. Now more than ever we need to be demonstrating the benefits of face-to-face communication at every opportunity."