1
general::
Be forced to resign, as in We were sure that Ted hadn't left of his own accord; he'd walked the plank. This metaphoric idiom alludes to a form of execution used in the 17th century, mainly by pirates, whereby a victim was forced to walk off the end of a board placed on the edge of the ship's deck and so drown. [Second half of 1800s]
American Heritage Idioms
2
general::
Phrase(s): walk the plank
Fig. to suffer punishment at the hand of someone. (Fig. on the image of pirates making their blindfolded captives die by walking off the end of a plank jutting out over the open sea.) • Fred may think he can make the members of my department walk the plank, but we will fight back. • Tom thought he could make John walk the plank, but John fought back.
McGrawhill's American Idioms And Phrasal Verbs