Two oil terminals in east Libya were forced to halt production Thursday by federalism backers, an AFP journalist at the scene and local sources said.
"The harbour is closed... The pumping and loading of oil has been stopped... The group that came were federalists," said Tumi Shakari, a supervisor at a major oil terminal in the port town of Ras Lanuf.
The action follows threats from a pro-federalism movement to boycott and sabotage the upcoming July 7 poll, which marks the first elections after a 2011 popular uprising toppled the regime of Moamer Kadhafi.
"A group of 15 people came around 9:30 pm (1930 GMT) and in a very peaceful and amicable manner asked us to shut down operations," the supervisor added.
"This group has certain demands that they want to see fulfilled and they have asked us to stop our work for 48 hours," he continued, adding that workers had to decided to comply to avoid an "escalation."
One of the central demands of the federalist movement is an equal allocation of seats in the 200-member national assembly due to be elected Saturday.
The interim authorities, on the basis of demographic considerations, allocated 100 seats to the west, 60 to the east and 40 to the south.
Ibrahim al Jadhran, a protest leader, said demonstrators had also shut the port of Al-Sidra, 35 kilometres (20 miles) west of Ras Lanuf, and were heading eastbound to the oil terminal of Brega.