Maritime Union of New Zealand national president Phil Adams, of Dunedin, said the union was still considering industrial action over KiwiRail's plans to reduce its engineering and design operations.
"We understand the wagons will come into New Zealand through Tauranga. It's a possibility we would consider not unloading them in support of our union brothers," Mr Adams said.
KiwiRail chief executive Jim Quinn said talks would begin by the end of next month between management executives and Rail and Maritime Transport union delegates over the proposal to cut 70 jobs.
Mr Quinn said he hoped relations with union workers would remain "professional".
A first shipment of about 135 flat-deck wagons was on the way from China to New Zealand and expected "anytime soon", he told the Otago Daily Times on Thursday.
Forty jobs are likely to be cut from the Hillside Engineering Workshop in South Dunedin.
RMTU delegates blame the job losses on the Government and KiwiRail's decisions to outsource major rail manufacturing contracts overseas.
Mr Adams told the ODT in January the Maritime Union was considering industrial action in protest at KiwiRail's initial decision to award a $29 million contract to build 300 open-top wagons to China's CNR Corporation.
KiwiRail subsequently outsourced another contract for 200 flat-deck wagons to China in April, before it announced its proposal to cut 70 jobs because of reduced workloads for its engineering and mechanical divisions.
The proposed job losses in engineering and design at Hillside, Woburn in the Hutt Valley, and Wellington were "the tip of the iceberg", Mr Adams said.
He expected further redundancies would follow given KiwiRail's trend towards outsourcing work overseas.
"How can we compete when this work is being built by Chinese slave labour?"
The union would consider "any method we can to help out" and support the plight of its RMTU brothers, he said.
Hillside-based RMTU national president Jim Kelly said no formal approach had "yet" been made to consider industrial action alongside the Maritime union.
He ruled out the likelihood of any immediate on-the-job strikes at Hillside, which would "defeat the purpose" as union delegates prepared to negotiate with KiwiRail about the proposed cuts.
However, stopwork meetings would take place at Hillside as the RMTU considered its options.
