Imposition of trade quotas for political reasons

International cartels enforced by governments
Imposition of quantitative trade quotas of a discretionary character
Discriminatory managed trade mechanisms
Surrender to "managed trade" or "fair trade" and you surrender to the rule of the strong against the weak. GATT has inadequacies aplenty but beside its alternatives it is a bulwark of sanity.
(E) Emanations of other problems