“07.11.69 The Office for Foreign Assets Control of the Treasury Department announced that it had reasons to believe that materials with nickel content and items made in Czechoslovakia could be wholly or partly made with or derived from nickel of Cuban origin. It was communicated that as from November 7, 1969, imports of materials and items containing nickel, made directly or indirectly from Czechoslovakia would be detained by Customs until their release from Customs or other provision were authorized by the Office for Foreign Assets Control, under the provisions of the Cuban Assets Control Regulations.” [Pro Embargo]
“Lyndon B.Johnson (D). Timeline,” Cuba versus Blockade: Cuban People’s website, 2007