The Mission to Seafarers charity says a last-minute appeal has been lodged against the decision of India's high court that apparently ended their ordeal.
Indian authorities arrested the 197-dwt support ship Seaman Guard Ohio (built 1984) in October 2013 for allegedly illegally entering its waters.
India had planned to charge them for not notifying the country of weapons on board.
But the men were freed in July and the case was then dropped.
They could now be detained again, however.
Canon Ken Peters, the Mission's director of justice and welfare, said: “This has been the most terrible ordeal for all the crew and their families, and I am baffled that this has happened now.
“It has been a complex case, but the high court judge dismissed all charges three months ago, so the men rightly presumed that they were at last free to go."
Crew member John Armstrong said: “Since the charges were dropped we were entitled to return home. Nothing in Indian law states that we can have our documents withheld by the authorities when we have been found innocent.
“Despite this, the magistrate court in Tuticorin overturned the high court’s dismissal of the case and ruled we were not allowed our travel documents or luggage, which is apparently still on the ship.”
Colleague Paul Towers said the men had not been paid for 11 months.
He added: “This has had a heavy financial effect on all of our families. I pray to God this will end soon.”
The six Britons among the men feel the UK government has not done all it can to bring them home.
