Changes to returns are subject to appeal by the taxpayer, including going to court. IRS changes are often first issued as proposed adjustments. The taxpayer may agree to the proposal, or may advise the IRS why it disagrees. Proposed adjustments are often resolved by the IRS and taxpayer agreeing to what the adjustment should be. For those adjustments to which agreement is not reached, the IRS issues a 30-day letter advising of the adjustment. The taxpayer may appeal this preliminary assessment within 30 days within the IRS.