As the 2026 tax filing deadline approaches, the National Taxpayer Advocate is warning Americans that recent changes to U.S. Postal Service ( USPS ) rules could unexpectedly cause mailed tax returns or payments to be classified as late—even if taxpayers believe they sent them on time. The Taxpayer Advocate says that new procedures governing USPS postmarks could undermine the long‑standing “timely mailed is timely filed” rule that many taxpayers rely on when submitting documents by mail. The