Wellington rail workers plan to strike on Thursday from 2am, for 24 hours, to defend their working conditions.

Wellington railway workers are to hold a 24-hour strike on Thursday.

The workers, employed by Transdev Wellington and Hyundai Rotem on Wellington's passenger rail network, have voted in favour of taking industrial action, saying they need to defend their terms and conditions of employment.

They plan to stop work for 24 hours, starting from 2am on Thursday.

STUFF Rail union general secretary Wayne Butson says the union has been trying to negotiate with Transdev and Hyundai Rotem since May. (File photo)

Metlink said on Tuesday night there would be no trains, and no bus replacements either at this stage, "although we are exploring options".

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It advised rail commuters to make alternative transport arrangements, "or consider not travelling at all".

Motorists and bus users should expect delays caused by heavy traffic, and should also consider making alternative arrangements, including travelling earlier or later, or not at all.

Parents and caregivers should re-evaluate their plans if children could not get to school during strike action.

Students sitting exams would need to factor train cancellations and road congestion into their travel plans, as should people travelling to Wellington Hospital or the airport.

On a regular weekday in Wellington, more than 30,000 passenger journeys were made by train, Metlink said. "With short notice, we are not able to source enough buses to transport this number of passengers."

The strike action comes after Transdev and Hyundai Rotem called for the removal of long-standing terms and conditions in the workers' collective agreement.

Rail and Maritime Transport Union general secretary Wayne Butson said the union had been trying to negotiate with the companies since May.

Transdev and Hyundai Rotem, who were multinational companies, had signed up to the conditions a year ago when they got the contract for Wellington's services, he said.

Now they were trying to increase profit by "squeezing frontline workers".

It would be the first industrial action since 1994 to affect the Wellington rail network for longer than two hours.

Metlink advised travellers to check www.metlink.org.nz regularly, follow @metlinkwgtn on Twitter, or call Metlink on 0800 801 700.