The Saudis have been blockading the port of Hodeida in Houthi held Yemen for a number of years. In 2017 they imposed a total blockade which caused widespread shortages of food, fuel and medical supplies. Humanitarian aid imports were impossible during this period.
As a result of UN pressure the Saudis partially lifted their blockade and now allow some commercial supplies into the port. This is facilitated by the UN Verification and Inspection Mechanism which checks cargos for weapons.
In December 2020 the Saudis imposed a fuel blockade on shipping bond for Hodeida port. This is having a disastrous impact on fuel supplies for hospitals, aid transportation, water and sanitation and is pushing up food prices.
The Saudis and Government of Yemen say that the Houthis were using fuel revenues to buy weapons and had reneged on an agreement to use duties to fund hospital workers and teachers (who have not ben paid for years)