Article 85 CISG
If the buyer is in delay in taking delivery of the goods or, where payment of the price and delivery of the goods are to be made concurrently, if he fails to pay the price, and the seller is either in possession of the goods or otherwise able to control their disposition, the seller must take such steps as are reasonable in the circumstances to preserve them. He is entitled to retain them until he has been reimbursed his reasonable expenses by the buyer.