How much commerce disruption equates an act of war, even if no shots are fired? I'm pretty sure blockading ports (as in cities where ships go, not network port

How much commerce disruption equates an act of war, even if no shots are fired? I'm pretty sure blockading ports (as in cities where ships go, not network ports) counts, so that's a starting point. But on the other hand, blockades do tend to be backed up by at least threats of actual physical violence, so.... ?