At the United Nations in New York it's considered "a nuclear option" for the Secretary General to invoke Article 99 of the UN charter as he did yesterday in a letter to the Security Council.
It’s a sign that the UN leadership feels it has run out of options trying to cajole and pressure the Council - the UN’s highest decision-making body - into action.
A spokesperson for the Secretary General called it a "dramatic constitutional move" intended to press Council members to demand a ceasefire, citing the "scale of the loss of human life in Gaza and in Israel, in such a short amount of time."
Article 99 is the only independent political power that a UN Secretary General has at their disposal.
"I think it's arguably the most important invocation," spokesperson Stéphane Dujarric told reporters at UN Headquarters, "in my opinion, the most powerful tool that he has."
In his letter to the Council, Mr Guterres warned that the situation in Gaza posed a serious threat to international peace and security.
He wrote that the population of Gaza - some 2.2 million people - were being forced into increasingly smaller areas and that nowhere was safe.
"Amid constant bombardment by the Israel Defense Forces, and without shelter or the essentials to survive, I expect public order to completely break down soon due to the desperate conditions, rendering even limited humanitarian assistance impossible," he wrote.
"An even worse situation could unfold, including epidemic diseases and increased pressure for mass displacement into neighbouring countries."
It is the first time that Mr Guterres has used Article 99 since he became Secretary General in 2017.
While indirect references to the Article have been made, the last time the special power was formally cited was in 1989.
The then Secretary General, Javier Perez de Cuellar, used it to press for a ceasefire in Lebanon’s civil war.
A decade earlier, in 1979, Secretary General Kurt Waldheim invoked Article 99 over the Iran hostage crisis, when 52 Americans were held at the US Embassy in Tehran after Iran’s Islamic Revolution.
Before that in 1971, Secretary General U Thant used the special power over the war in East Pakistan, which subsequently became Bangladesh.
And in 1960 then Secretary General Dag Hammarskjold used it during the Congo crisis.
The question now is whether this symbolically dramatic move by the Secretary General will shake the UN Security Council into action.
After all, the same divisions remain today that were there before the Secretary General put pen to paper.
The United States, Israel’s staunchest ally on the Council, has not backed a call for a ceasefire, arguing that it would allow Hamas to regroup.
But last month, it did abstain from a resolution calling for humanitarian pauses, allowing for the first successful passage of a Council text on the war, 40 days after the October 7th attacks and Israel’s bombardment of Gaza began.
Israel reacted bitterly to the Secretary General’s invocation of Article 99 yesterday calling it a "new moral low" which proved his "bias against Israel."
A draft resolution prepared by the United Arab Emirates, a non-permanent member, is already circulating among Security Council diplomats and a vote could take place as early as tomorrow.
But it is unclear whether the text which calls for an "immediate humanitarian ceasefire," will get the requisite nine votes to be adopted. If it does get enough yes votes, the US could be forced into using its veto again - something it will not appreciate, according to analysts.
"I still do not think that the US will alter position," Richard Gowan, UN Director with the Crisis Group, a think tank, told RTÉ News.
"If it has to veto the text it will. That will make the US look bad once again, and the Americans will be unhappy with Guterres for helping put them in a difficult position," he said.
