I had a similar situation. 'Bout 15 years ago I was in charge of tech marketing for a fun mid-sized company and we were going to have a one-evening event to promo our technology in San Francisco in a hotel two miles away from a major trade show. We had everything set up when I got a call three days beforehand from the hotel manager telling us that the contract they had with major trade show prohibited them from holding our event and they were cancelling.
I mentioned that our lawyer was going to call him. Lawyer later called, told them that since this was his (the hotel manager's) decision that our action would be against not only the hotel, but also against the hotel manager, personally. Meanwhile I called the PR director for the major trade show, who was apologetic but she said in a semi-evil voice "this is how its done". Very politely I told her that we had about a dozen members of the press confirmed to attend, and when I called the press on the phone (not email) to tell them I was being forced to cancel our event should I give the press her name?
Well she stuttered like porky pig and said she'd get back to me. A few hours later I got calls from both the hotel manager & the PR person telling me my event was on. After that I invited our lawyer to each event with the promise of good food and a fun time.
If I was IGEL, I would have brought my lawyer just in case, and when their goons started tearing things down I'd have my lawyer, business card in hand, identify himself to the minimum-wage goons and ask to see their badges for guaranteed PERSONAL legal action.
Can't fight a big company, but you can take down their people one at a time.