An advocate, Biara Touakin, who is based in Fiji, said a ship typically visits each month, but the last one, on January the 6th, only contained enough food for about two weeks.
The more than 300 people living on Banaba depend almost entirely on food sent from Tarawa.
The island was decimated by phosphate mining in the first half of the 20th century, and it no longer has fruit bearing trees that could supplement the people's fishing.
Mr Touakin also said the desalination plant installed late last year continues to produce brackish water.