KiwiRail's Hillside workshops in Dunedin must be kept open, Labour says.
The company has put the workshops up for sale and is considering closing them if a buyer can't be found.
Labour leader David Shearer visited the workshops on Monday and says they're a national asset.
"It's time we got patriotic about our manufacturing industry," he said.
"It's one of the pillars of our economy... it also keeps New Zealanders working here rather than heading across the Tasman for jobs and better opportunities."
Mr Shearer says countries like Australia, Singapore and the United States have procurement policies that recognise those wider benefits.
"We should be doing the same - Hillside is the backbone of Dunedin's manufacturing industry."
The Rail and Maritime Transport Union, which represents the workshop's workers, says it would be "madness" to close them.
General secretary Wayne Butson says the union is confident it can work with a buyer and make the workshops a success.
"It would be madness to shut down Hillside... what would make sense would be to give Hillside more rail work, such as building rolling stock."
NZN