The venue has a reputation for being....shit (they booked Gavin McIness on one of his little tours a while back). Each year, someone in my city puts on a metal fest there and lots of nazi bands from Europe come over and play, and apparently openly fascist shit is sold at the merch booths.
Last year I emailed the local city council about it. They were useless. Right now, I'm about to email the music section of my local big paper about it, AND OFFER RECIEPTS (since I can easily compile a good amount of evidence of nazism) to see if they wanna shed some light on it.
What else can I do short of 
?
If your city or region has an active antifascist group, inform them. My hometown used to have regular nazi gatherings, now they've all been doxxed and had their lives ruined. They are ruthlessly effective.