"We've been trying to negotiate with Transdev and Hyundai since May this year, and they've stalled every single step of the way.
"We all regret the disruption this will cause for Wellington commuters, and we encourage them to ask the regional council, and their mayors, some hard questions about why big international companies are being allowed to run down good Wellington jobs."
Butson said the two multinational companies were demanding the removal of long-standing terms and conditions in the collective agreement.
He said strike action was the only option they had left "to get the boss to sit down and be reasonable".
Metlink's manager of rail operations Angus Gabara said they couldn't put on that many replacement buses for such a high-use service.
He said commuters would need to make other travel arrangements, and if possible, not travel at all.
"Commuters, people with medical appointments, and students sitting exams who have to travel, should allow extra travel time due to the disruption this strike will cause.
"Bus services are operating as usual but we expect them to be under significant pressure with increased passengers.
"Motorists should also expect delays because of the extra cars that are expected to be on the roads."
Gabara said they were still looking at options to help travellers who had no alternatives ways of getting around.
He said any last-minute changes would be posted on metlink.org.nz.
