Article 189 provides a standard procedural protection for deadlines. It stipulates that if a specific deadline for any tax procedure (such as filing a return or submitting an objection) falls on an official holiday, the time limit is automatically extended to the first following working day. This ensures that taxpayers are not penalized for the closure of government offices or automated systems during national holidays, providing a fair and consistent timeline for all legal and administrative actions required under the Income Tax Law.