on pain of

on pain of

With the threat of undergoing something extremely bad or unpleasant as a punishment. Often used in the phrase "on pain of death." The prisoners were forced to march on pain of death from the POW camp across the burning desert. On pain of having our pay docked, we were told we had to come in every Saturday until further notice to take care of the backlog of work.
See also: of, on, pain

on pain of

Also, under pain of. Subject to the penalty of a specific punishment. For example, The air traffic controllers knew that going on strike was on pain of losing their jobs . At one time this idiom often invoked death as the penalty, a usage that is largely hyperbolic today, as in We'd better be back on time, under pain of death. [Late 1300s]
See also: of, on, pain

on/under pain of something

(formal) with the threat of having something done to you as a punishment if you do not obey a command: They were forbidden on pain of death to talk to any of the other prisoners.We were told to pay within three days, on pain of a €1 000 fine if we didn’t.
See also: of, on, pain, something
References in classic literature ?
In vain had she remonstrated, in vain she had mingled his wine with water: her arguments and entreaties were a nuisance, her interference was an insult so intolerable that, at length, on finding she had covertly diluted the pale port that was brought him, he threw the bottle out of window, swearing he would not be cheated like a baby, ordered the butler, on pain of instant dismissal, to bring a bottle of the strongest wine in the cellar, and affirming that he should have been well long ago if he had been let to have his own way, but she wanted to keep him weak in order that she might have him under her thumb - but, by the Lord Harry, he would have no more humbug - seized a glass in one hand and the bottle in the other, and never rested till he had drunk it dry.