"The mystery of life isn't a problem to solve, but a reality to experience"
Only the regulars in that stack are eligible to be removed if that power does not discard a card.
(17) 4 / Army Mutiny
Target a stack of units controlled by one major power for mutiny (units on the Armada are not eligible). All mercenaries in the stack of that target power are removed from play. Target power also loses all regulars unless they discard a card or treasure immediately. Value of card/treasure determines number of regulars kept: 1 CP=2 regulars 2 CP=4 regulars 3 CP=6 regulars 4 or more CP=all regulars retained. Add unrest to the target space and one adjacent space. [FAQ: Target power gets to choose which regulars are retained and which ones lost.]
The card referes to all the mercenaries in the stack being lost and then the target could also lose all their regulars (in the stack), unless they discard a card.
Otherwise it would be game breaking if played against an opponent with no cards!