My understanding from some things I’ve read recently is that, if the action taken against your account was a suspension, TL3 is not reobtainable. There’s a thread somewhere on the forums that seems to document the new layout pretty thoroughly, I’ll see if I can find it.
If the action doesn’t line up with either of those two bullets, I think it’s at least safe to say that you’re good to try reacquiring it, but I’m not aware of anything being definitively stated by Blizzard.