Not everybody is a fan of the Stop Card.
Why slow down play unnecessarily when it goes 1NT Pass 3NT and you have no intention of calling?
Alas, it is not possible to draft a regulation that differentiates between a pre-emptive call, designed to give the next player a problem, and a full value leap to game.
The Stop Card is a blessing when you do have a problem: it gives you time to think without putting partner under ethical pressure.
Be grateful that it exists when you do have a problem; and respect it when you do not.
♣ Always play the Stop Card before making a jump bid
♣ Always pause when RHO plays the Stop Card
The Laws of Bridge do not yet cover the use of the Bidding Box, but there are Regulations:
6 Before making a jump bid (i.e. a bid at a higher level than the minimum required) a player must place the Stop card in front of him, then place his call as usual, and eventually remove the Stop card. His LHO (left-hand opponent) should not call until the Stop card has been removed. The Stop card should be left on the table for about ten seconds, to give the next player time to reflect. It should not be removed prematurely.
7 After a jump bid, the next player must pause for about ten seconds before calling. It is an offence either not to pause or to show indifference when pausing. If the Stop card has been removed prematurely or has not been used an opponent should pause as though the Stop card had been used correctly.
(SBU Bidding Box Regulations, 2009)
You can find these Regulations, along with other important documents, on the SBU website at sbu.org.uk/index.php/council/laws-ethics.