noun
warning letter; written warning
A formal written notice warning of a violation, infringement, or unacceptable behavior, often used in legal, business, or official contexts.
著作権侵害の疑いで、会社に警告状が送られた。
A warning letter was sent to the company for suspected copyright infringement.
再三の注意にもかかわらず改善が見られないため、警告状を発行した。
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).