Federal regulations require importers, exporters, or their agents, to submit import and export information for all merchandise shipments above the established exemption levels. Exemption levels are $2,000 for imports (or $250 for certain quota items), and $2,500 for exports to countries other than Canada. The U.S. Census Bureau has determined that not all required documents are filed, particularly for exports, as import information is subject to greater scrutiny by U.S. Customs and Border Protection in relation to the administration of tariffs, quotas, and other enforcement activities. Goods withdrawn from Foreign Trade Zones (FTZs) for exportation, and exports of U.S. goods through Canadian ports en route to other destinations are two examples of commonly unreported shipments that can lead to errors in export statistics. Undocumented foreign merchandise entering FTZs, which should be included in import trade statistics under general imports, is an example of undocumented import data that can contribute to the problem of import under coverage.