At the Port of Nantes – Saint Nazaire, customs officers carry out checks on the physical flows of goods both for import and for export. They collect duties, taxes and levies on behalf of the European Economic Community, the French State and the Port.

Customs officers enforce the regulations relating to foreign trade, notably those concerning qualitative and quantitative restrictions on trade exchanges. They watch over the port areas and vessels and protect French national territory against the smuggling of prohibited goods presenting a human hazard.

The manifest (or description of the vessel’s cargo) forms the basis of the customs declarations and checks, until the goods are "released" (made available to their consignee).