Reviewed by Sasha Božič, Licensed Customs Broker

CBP Form 19 is the protest. It is how an importer formally challenges a CBP decision under 19 USC 1514, most often the liquidation of an entry. Once an entry liquidates, a Post-Summary Correction is off the table, and the protest becomes the main administrative route to get duty back.
Section 1514 lists the decisions a protest can contest. The ones importers use most:
A protest must be filed within 180 days of the date of liquidation, or within 180 days of the decision being protested when no liquidation is involved. CBP sends no reminder. Once the window closes, the decision is final and the duty stays paid.
Most protests are filed electronically through the ACE Protest module. The importer, its licensed customs broker, or its attorney can file. A single protest can cover several entries when they involve the same issue. Each one needs the entry numbers, the decision being contested, and the legal and factual basis for the claim.
CBP generally has two years to allow or deny a protest. Any time after 90 days from filing, you can request accelerated disposition. If CBP doesn't act within 30 days of that request, the protest is treated as denied, which opens the path to court. You can also request further review, which moves the protest to a higher level within CBP. A denied protest can be challenged at the Court of International Trade within 180 days of the denial.
Timing decides it. Before liquidation, a Post-Summary Correction is usually the faster fix. After liquidation, the protest is the tool. Post-Summary Corrections and protests both sit inside Caspian's post-entry audit, which checks every filed entry and routes each error to whichever path is still open.
IEEPA duties follow their own track. Most are refunded through CBP's CAPE process, and protests preserve the claim on entries CAPE can't reach yet. See IEEPA tariff refunds.