Libyan Prime Minister Ali Zeidan [Zidan] has threatened to use force to prevent guards striking at the country's main ports from selling oil independently.
He said any ship approaching the ports which does not have a contract with Libya's official oil company would be "bombed from the sea or the air".
The workers have been striking over pay for several weeks.
Officials say the protests have caused a drop in Libya's oil exports and are harming the economy.
"If the blockade of these oil terminals continues, the state will be obliged to use its power, and all the forces at its disposal, including the army," Mr Zeidan warned.
He said that the ports of Zeitunia, Brega, Ras Lanouf and Sedra had been closed by the protesters' action.
Oil Minister Abdelbari al-Arusi said that Libya had lost about $1.6bn (£1bn) in revenue since 25 July because of the disruption.
Export problems have reduced Libya's output to just 500,000-600,000 barrels per day compared to the country's production capacity of 1.6 million bpd representing over 1.5 percent of the global oil output.
That in turn has been putting pressure on oil prices in global markets in recent weeks.
(Sources: BBC, Reuters)
