The Rail and Maritime Transport Union is worried dozens of old train units could be sent to landfill.
The Ganz Mavag trains were replaced by Matangi trains in 2016 but not all of them have managed to be sold on.
The Greater Wellington Council said it was unlikely they would sell the remaining passenger trains.
Rail and Maritime Transport Union Secretary Wayne Butson said he was appalled and they should be repurposed.
"One of the things we're desperately short of in New Zealand at the moment is passenger rolling stock and over the years we've got very good at refurbishing passenger rolling stock and so I just don't understand why we can't refurbish these vehicles," he said.
There should be a conversation with ratepayers about their fate and believed if they weren't sold overseas they could be used elsewhere in New Zealand, he said.
However, the Greater Wellington Council said they were continuing to investigate options for disposal and nothing was being ruled out.
One unique solution had been suggested.
Solscape offers accommodation at its retreat out of repurposed train carriages in Raglan and co-founder Phil McCabe said there was a real market for them.
"A few years ago we were upgrading an area of our property where we had three trains and we didn't actually advertise them but the word got out and we had 20 or 30 phone calls over the space of a month.
"If you put these trains on Trade Me I can guarantee they would go within weeks," he said.
It would be foolish not to consider it, he said.
"House prices the way they are and construction prices and people struggling to get into homes, it's a good first option for young people and people wanting that sort of lifestyle, it's a good example of upcycling," he said.