Limitation for imposing penalties sets time limits and hearing safeguards for tax penalty orders. Section 275 fixes a six month limitation from the end of the quarter in which the triggering event occurs for passing orders imposing, enhancing, reducing, cancelling or dropping penalties, with triggers including completion of proceedings, receipt of appellate or revisional orders, or issuance of notice. Penalty orders may be revised to give effect to assessments altered on appeal or revision, but only after affording the assessee a hearing and within the same limitation period. Time taken for rehearing under section 129 and periods of court granted stays are excluded from the limitation computation.