The legality of blockades is a very messy topic. The international treaties that cover these situations are complex and vague to begin with, plus they are relatively old and don't apply well to the modern world.

I see at least three grounds for questioning Israels blockade. The one I've seen quoted elsewhere the most is that the 1997 amendment to the Geneva convention prohibits collective punishment against civilian populations. Essentially, Israel can't impose a blanket blockade, they have blockade only military goods. However, Israel has not signed that particular protocol, so it's legal applicability to Israel is questionable.

The second is also based on the Geneva Convention, the 1949 Fourth Geneva Convention which regulates the behavior of occupying powers. Israel has been consistent in saying that since they have removed the ground force from the Gaza Strip they are no longer an occupying power. But many experts disagree, saying that Israel's control over the Gaza strip amounts to an occupation.

The third, which I have not seen raised anywhere else but seems obvious to me, is that the UN charter makes it illegal. Under the UN charter countries are only legally allowed military action in self-defense the face of armed attack, except when the US security council authorizes it. Under that rule, Israel is only allowed to blockade Gaza during periods of missile attacks.

Jay

Though apparently there are provisions in the treaties to cover blockades of land locked nations.

More to the point, there is an obvious gap in the treaty over time frames. The treaty doesn't say anything about response times or how long the Security Council has to act or how long your are justified in retaliating after an attack.

You obviously can't read it as being an elaborate game of green light/red light where you have to stop the moment the other side says they are stopping. But at the same time you can't sensibly read it as lasting forever either, Iran can't justify invading Iraq now over the invasion Saddam ordered of Iran.

Ultimately it's a matter of political pressure.

Jay