Illinois Notice of Disallowance of Claim is a form issued by the Illinois Department of Revenue (IDOL) for taxpayers to inform them that their claim for a refund or credit has been denied. This form notifies taxpayers that their claim has been disallowed due to certain reasons, such as failure to provide complete and accurate information, failure to meet filing requirements, or the claim being barred by law. There are two types of Illinois Notice of Disallowance of Claim: (1) Notice of Disallowance of Claim for Refund or Credit; and (2) Notice of Disallowance of Claim for Interest or Penalty Waiver.