Yemeni coastguards blocked ports on Sunday to protest against the government's failure to pay financial benefits they said it had promised, halting most shipping.
Port officials said the guards prevented workers from entering four main ports, including Aden in the south, Hodeidah in the west and the Red Sea ports of Mokha and Saleef.
"Movement has completely stopped in almost all ports," Sharaf Mohammed, a ship captain at Hodeidah.
Yemen has slipped into a state of chaos during a year of unrest. Former President Ali Abdullah Saleh has been ousted after 33 years of rule and replaced by his deputy, Abd-Rabbu Mansour Hadi, under a deal brokered by Yemen's rich Gulf neighbours.