warning letter; written warning
A formal written notice warning of a violation, infringement, or unacceptable behavior, often used in legal, business, or official contexts.
A warning letter was sent to the company for suspected copyright infringement.
Since no improvement was seen despite repeated warnings, a written warning was issued.
注意書 is a written notice or caution, often less formal and not necessarily implying a violation; 警告状 carries a stronger, more formal tone of warning.
Compound of 警告 (warning) + 状 (letter, document).