Detention and seizure of goods: release on payment of tax and prescribed penalty, or on furnishing security; hearing required. Section 129 permits detention or seizure of goods, conveyances and related documents when transport or storage contravenes the Act, but requires serving an order before detention. The proper officer must issue a notice specifying tax and penalty and may order release on: (a) owner's payment of tax and a penalty equal to the tax (with prescribed treatment for exempt goods); (b) payment where owner does not come forward of a penalty assessed at fifty per cent of the goods' value reduced by tax paid (with prescribed treatment for exempt goods); or (c) furnishing prescribed security equivalent to the amount due. An opportunity to be heard is required and payment concludes proceedings; failure to pay within seven days leads to further proceedings, with a shorter period allowed for perishable or hazardous goods.