letter of advice; written recommendation; advisory letter
A formal written document that advises, recommends, or urges a certain action. Often used in official, legal, or business contexts.
The company sent a letter of advice urging the client to make the payment.
通知書 is a general written notice, whereas 勧告状 specifically conveys advice or a recommendation, often with an implied expectation of action.
Compound of 勧告 (advice, recommendation) and 状 (letter, document). The exact historical derivation is uncertain, but the word follows a common pattern for formal written communications.