Several decades ago when my Dad was still working, he said they quit displaying at trade shows held at Chicago's McCormick Place - the facility insisted that you would have to hire the on-site union electricians for everything, even to change a light bulb in your display.
Even though they were on-site, you STILL were billed for round/trip travel time from wherever their home office was, mileage, two (2) electricians, fuel surcharge, etc. It could easily run $500.
To change an <expletive deleted> light bulb you could walk over to and change yourself in 30 seconds.
Exhibitors used to watch out for union "observers" and change their own bulbs . . . but then, overnight, bulbs started disappearing from displays. Bleeping crooks.
I used to be involved in a publishing company that exhibited at least once a year at McCormick. Amen to all you say here. The place was a shameless cathedral of cold-blooded exploitation by the unions. All rather ironic given that the trade show involved was focused on arguably the most competitive industry in the world.