The proper form for a pass seems to me to have been specified in exactly the same (minimal) manner as that for a double or a redouble in L18A. L20A and L74C1 also seem to be relevant. To answer your initial question, I think I would say "maybe, it depends on the circumstances". It's not uncommon to accept violations of proper form when spoken bidding is used: "No bid" "No" "Four hartleberries" "Three of the house" I would put the onus on the caller to ensure that it's not misunderstood and doesn't pass UI. Otherwise, sanctions may be appropriate. Edit: Having looked further, it seems you were referring to L19 and there you are correct. However, I wonder if that might have been deliberate to allow Brits to say "No bid" rather than "Pass", as the Orange Book permits (without reference to the Laws) in 7C2: "a player can use “pass” or “no bid” but should not change from one to the other during a session".