bus A 30-day letter is issued to the taxpayer upon audit: 1. if the taxpayer agrees with the Service's proposed adjustments and signs a waiver of his or her right to notice of deficiency. 2. if the taxpayer does not agree with the Service's proposed adjustments to inform the taxpayer of his or her right to appeal within 30 days. 3. if the taxpayer does not agree or partially agrees with the Service's proposed adjustments to inform the taxpayer of his or her right to appeal within 30 days. 4. if the taxpayer does not agree or partially agrees with the Service's proposed adjustments to inform the taxpayer of his or her right to file a protest in the Tax Court within 30 days