It looks like most of President Yoon’s cabinet had no idea about the martial law decree and he called them into a meeting that night just to consolidate them before declaring it:

A brief, five-minute Cabinet meeting took place between 10:17 p.m. and 10:22 p.m. in the presidential reception room, apparently without due process or any official record, according to data from the Ministry of Interior and Safety submitted by the presidential office.
Yoon, who came into the meeting but did not even sit down, abruptly left the meeting. At 10:23 p.m., he began reading his statement — without the presence of Cabinet members or reporters. The live televised address culminated in the declaration of martial law at around 10:28 p.m.
Minister of Agriculture, Food and Rural Affairs Song Mi-Kyung vividly recounted that some of those present at the five-minute Cabinet meeting on Dec. 3 were completely blindsided, leaving them powerless to intervene or stop him from making it public.
“(The president) briefly entered the room and then left. After he left, those who were seated were taken aback and asked, ‘Where did he go?’ At that moment, someone played a broadcast on their phone, and his voice came through. That’s what happened,” Song said during the Dec. 11 plenary session of the Assembly, recalling that the Cabinet meeting never formally concluded — there was no declaration signaling its end.
“It wasn’t even possible to grab hold of him or physically intervene in any way. I am truly sorry for this.”
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