Before any letter is placed in your file, you must be given an opportunity to read it and acknowledge its receipt by signing it. If the letter is negative, you should consider writing a response, detailing why you disagree with its contents. There is no time frame by which your response must be written. You should speak with your chapter leader, who can help you write an appropriate response and advise you on any other possible course of action, including procedural matters that may be grievable. The response should be attached to the original letter in your file; your supervisor cannot respond to your response.
If a letter is written for your file outside the contractual time limits, you have a right to grieve to have that letter removed. In addition, an arbitrator has ruled that you have the right to grieve “if material is placed in a teacher or employee file under circumstances that are alleged to constitute a violation of substantive Collective Bargaining Provisions.” In other words, if the letter violates a substantive part of the contract, you can grieve the letter under that contractual article.
If the letter is not used as the basis for disciplinary charges within three years, you can and should have it removed from your file. Talk to your chapter leader about how to do this.