/ˈlɛtər bɪˈfɔr ˈækʃən/ – Phrase
Definition: Thư cảnh cáo trước khi kiện.
A more thorough explanation: a formal notice demanding that the recipient perform a legal obligation to avoid being taken to court, eg pay a sum of money or perform an obligation under a contract
Example: The law firm advised him not to send a letter before action unless he had the time and resources to take legal action.