Even without referring to Egypt's military moves, the government of Israel insisted that it could lawfully invade Egypt because of Egypt's restrictions on passage through the Straits of Tiran into the Gulf of Aqaba. When Egypt announced these restrictions on May 22, Prime Minister Eshkol called them a “blockade” and an “aggressive act against Israel.” Eshkol told the Knesset, “We are confronted with a fateful hour.” A few days later, Eshkol laid a legal basis for military action: “The Government of Israel expresses its view that the blockade of the Straits of Tiran against Israeli shipping is the equivalent to aggression against Israel. We shall oppose it at the proper time, in accordance with the right to self-defence vested in every State.” Eshkol was saying that Israel could lawfully attack Egypt at a time of Israel's choosing.

Eshkol's argument about aggression rested on two assumptions. The first was that Egypt was legally obligated to allow passage through the Straits of Tiran. The second was that violation of this obligation rose to the level of aggression, giving rise to a right of self-defense. The issue of passage through the Straits of Tiran enjoyed a definite pedigree as a legal controversy. The issue pitted the rights of Egypt, as a state bordering the Straits, against those of Israel, as a state with a coastline on the Gulf of Aqaba, that coastline (at Eilat) being reachable from the open seas only via the Straits.