How do I choose between Form 3949-A and Form 14157?

Choose based on who or what you are reporting.

Use Form 3949-A when the main issue is an alleged tax-law violation by an individual or business. Common exam cues include unreported income, false deductions, failure to file, failure to pay, or failure to withhold.

Use Form 14157 when the main issue is misconduct by a tax return preparer or preparation business. Common cues include no PTIN, no paid-preparer signature, refusal to provide a return copy, improper use of consumer software for paid preparation, or falsely claiming professional credentials.

If the preparer's conduct affected the taxpayer's own return or refund, add Form 14157-A to the analysis. The forms do not fix the taxpayer's return by themselves; the taxpayer may still need a notice response or amended-return analysis.