Shut-In

If you are the defender, play this tactic during the
Priority phase, after Roll for Priority, but before Ready
Fighters. If you are not the defender, discard this card
and draw another.
Every open door on the battlefield immediately
closes and becomes locked. If a door does not
have a terminal, then it can only be opened by
the Force Door action or targeting it with attacks.
If there are fewer than 3 door on the battlefield,
you may discard this tactic and select another.