That's really weird. I've heard of people quitting to join a competitor being warned that this burns their bridges, and I've heard of people being fired or laid off and told that when the company is hiring again it would not be interested in hiring them back. But I've never heard of someone being laid of or fired and told that if they were ever hired back, and the people who did the laying off or firing found out, they'd make sure the person is fired again.

The only thing that comes to mind where I'd expect that would be if they suspected you of some serious criminal or unethical or immoral activity, for which they either did not have enough evidence to bring in the authorities, or did not want the publicity. Maybe someone in your group was stealing and made it look like it was you? Or some rival whispered some accusations like you touched children at the company picnic or were putting the moves on the CEO's wife? Ot someone overheard you talking about what you were planning to do in a FPS game, and thought you were talking about the real world and they are afraid you are a future office shooter and don't want it to be at their office?

Did they give you any reason why they want to make sure you will never be back, or was it a surprise to you?

No criminal or any such activity. Not so good performance was the reason. Was dealing with some family issues at the time.

I don't think publicly traded companies can do that.

Pretty sure an internal blacklist is completely kosher... sharing it, on the other hand, is almost never legal.

The one that gave me that letter was a publicly traded company.