The Rena's crew would have been "terrified" when they issued a mayday, forcing their evacuation from the stricken ship, the maritime workers union said.
The 17 mostly Filipino crew members issued their call when the ship crushed the reef on which it was resting in the early hours of yesterday and shifted back a few degrees from its 10-degree list.
Maritime Union general secretary Joe Fleetwood said he did not accept official advice that the mayday was precautionary, and said the crew would have been fearing for their lives.
"It wouldn't have been a precautionary thing. As soon as you hit that button you're in distress. They probably feared for their safety, thinking this vessel's going to snap in half or roll over and kill everyone on board.
"I guarantee they would have been terrified."
Mr Fleetwood said that if it had been a New Zealand crew they would not have stayed on the vessel for the six days since the Rena struck Astrolabe Reef off Tauranga.
"If that was a New Zealand crew they would have been off the ship straight away. If that was an Australian crew they would have been off and done. They're Filipinos, and what I believe is they're treating them with contempt and telling them 'just stay there and do your job'. I've called for Maritime New Zealand to release all their reports so we can know who made all these decisions."
Maritime NZ said the crew would go back onto the ship once it was deemed safe to do so, but Mr Fleetwood doubted this would ever be the case.
Mr Fleetwood said he had been calling on the Government to buy an emergency oil spill response vessel "for years" but to no avail.
"Now we're caught with our pants down."
Team in charge
Who is organising the response?
* Two ministers at the top. Steven Joyce (transport) and Nick Smith (environment), both in Tauranga.
* Maritime NZ is the lead agency and reports to Mr Joyce.
* Ministry for Environment is dealing with environmental effects and cleanup.
* Ministry of Transport responsible for marine aviation and sea transportation
* Department of Conservation helping with beach cleanup
* Ministry of Defence personnel called in to help.
Local bodies / firms
* Bay of Plenty Regional Council, Tauranga City Council and Western Bay District Council providing maritime staff, science and engineering experts, emergency management, IT, communications and logistics.
* A salvage company working on behalf of boat owners and insurers.