something that you say or do as a warning to sb about what might happen if they do not change, etc.
A SHOT ACROSS THE / SB'S BOWS
Meaning of A SHOT ACROSS THE / SB'S BOWS in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005