It's pairs and no one is vulnerable.
You open 1♣. Unfortunately as you do so, you notice that your RHO is the dealer. LHO doesn't accept, and RHO opens 2♦ (natural weak).
If you bid 3♣ partner will be barred for one round, if you do anything else, partner will be barred for the remainder of the auction. What would you bid?
(It occurs to me now that this ruling might not be correct but I didn't argue the matter at the table).