All-in Question (rule clarification)

[bostondave]

We had this situation come up in my home tournament last night. The tournament is a $10 buy-in NL Hold 'em Tournament.

Let's say there are three players left. Big Stack 1 (BS1) is on the button w/T5000 and first to act preflop. Big Stack 2 (BS2) is in the small blind w/T5000, and Short Stack (SS) is in the big blind with T1000. Blinds are T100/T200

BS1 makes the total bet T800 (a raise of T600). BS2 calls, and SS moves all-in for a total of T1000. Can BS1 re-raise here, or does SS's all-in need to constitute a full raise? I tried using the search function, as well as reading a couple of other sites, but I got a variety of answers. Is there a definitive answer, or does it vary tourney-to-tourney?

Thanks in advance,
-Dave