Originally Posted by ToV
They were worried about their license and serving a beer that didn't come through a commercial brewery or a licensed distributor, plus liability if something should happen.
Indeed we had the same issue. They were also concerned about their lost income if we didn't purchase our booze from them. We were sneaky about it, but still managed to kill 4 kegs and many bottles over 3 days.
Some venues will require a 'convenience' fee if you bring in your own stuff.