國會裡的最高等級動員
這一支就是那張通知單本身，畫面沒有被借走，也沒有被比喻化。
noun · C1
In British politics, an order from the leaders of a political party telling their MPs that they must be in Parliament for a vote and must vote the way the party has decided.
三線動員令
核心畫面
Picture a weekly notice from party managers landing on a British MP's desk. Every item on it is : one line for 'come if you can', two for 'we would like you there', three for 'you are coming and you are voting our way'. The number of lines is the amount of pressure, and three is the top of the scale. Everything this phrase does in English grows out of that one picture of a line drawn three times under an instruction.
可以想成英國議員桌上每週收到的一張通知單。上面每件事都畫了底線：一條線是「有空就來」，兩條線是「希望你到」，三條線是…更多收起
可以想成英國議員桌上每週收到的一張通知單。上面每件事都畫了底線：一條線是「有空就來」，兩條線是「希望你到」，三條線是「你一定要到，而且要照黨的意思投」。底線的數量就是壓力的大小，三條是最高的一級。這個片語在英文裡做的每件事，都可以從「在指示底下畫了三次線」這個畫面長出來。From the word’s history
The name is literal: party managers send British MPs a weekly document called 'the whip', and the most important votes on it are underlined three times.
這個名字是照字面來的：英國黨團每週發給議員的文件就叫 the whip，上面最重要的表決會被畫上三條底線。
Wiktionary entry for “three-line whip” (evidence packet): “From the triple underlining of very important votes on ‘the whip’ — a document detailing upcoming business distributed weekly to British MPs by party managers.”
Two branches
借來開玩笑的「不准缺席」
同一張通知單被搬出國會，貼到家裡的冰箱或辦公室的行事曆上，力道留著，場景換掉。
noun · C1
A very firm instruction that you must come to a meeting or event, or must take part in it, used away from politics and usually as a joke.
不准缺席的強制令