Under the AIM Act, importers of bulk hydrofluorocarbons must hold sufficient EPA-issued allowances to cover each shipment before it enters US commerce. Allowances are allocated annually and can be transferred. Importers without adequate allowances cannot legally import covered HFCs, so securing allowances well ahead of shipment is essential.

HFCs (hydrofluorocarbons) are fully saturated fluorinated derivatives and classify under subheadings 290341–290349. HFOs (hydrofluoroolefins) are unsaturated fluorinated derivatives and classify under subheadings 290351–290359. The presence of a carbon-carbon double bond in the molecule is the chemical distinction that drives the classification split.