Do you get any floating text before they turn hostile? The first things that come to mind would be bringing Marcus in if they aren't fans of mutants, but most NPCs like that will tell you about it before attacking. That should also be the case if you run in with your weapon drawn.
Other than that, I guess there could be some kind of relation if you've worked some of the quests related to who controls New Reno and how that family treats Redding? Far fetched maybe, the only one in redding I remember is openly pro-Reno is the guy that runs the morningstar mine, I think.
Thanks, Dead Guy. I did do a lot in New Reno before coming back and finding this nasty surprise (because I had not finished Redding quests), but I actually gave the chip to the pro-Reno guy, so I don't think that's it. Also no mutants in tow, just Sulik and Vic. I have a feeling I looted something I should not have, but again, I was here so many game hours (and real hours!) ago, I have no idea what it was, and even if I did, I would not want to lose all this progress just to save that quest.
I also tried entering with guns stowed, same result. And there was some text spoken by the guards before they turned hostile. Usually something like "Ok, we told you this would happen!" or something to that effect. "That's it! You're going down!" Wildly paraphrasing, but obviously they had warned me before (or someone that LOOKED like me!

)
I guess my options at this point are
1. Abandon quest and that sweet, sweet loot - don't ever go into the Ace Casino again
2. Go Mad Dog and engage the guards, kill them, resulting in a city wide death match (I assume)
Any other options or suggestions, I am open to!
Thanks