on pain of

on pain of something

(slightly formal)
at risk of experiencing something bad She says she was asked to approve the report on pain of losing her job.
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
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.