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McDonald's has offered to guarantee workers 80 per cent of their rostered hours, but Unite Union director Mike Treen said that offer was meaningless because the company did not make the rosters public.
In Auckland, protesters gathered under the shadow of a giant inflatable rat to rally against the contracts.
A noisy crowd of about 180 fast food workers and supporters gathered at Britomart at midday before marching up to McDonald's on Queen St, and further up the street to Wendy's.
Flatmates Nicole Vatu, 30, from the Clendon McDonald's branch, and Lucy Tautagi, 19, from the Manurewa branch, said they both worked about 30 hours a week but both wanted 40 hours.
"They just don't give out enough hours of work. I come to all my shifts, yet they don't give me any more hours," said Ms Tautagi.
Both are still on only $14.80 an hour after two years and three-and-a-half years working for the company.
Also at midday, more than 50 people gathered outside McDonald's in Manners St, Wellington, where protesters held placards aloft and chanted into megaphones.
Maddie Taylor, who works at McDonald's Basin Reserve, said a colleague also wanted to come to today's strike, but could not afford to take the two hours off work.
"She needs everything she gets."
Mrs Taylor was thrilled with the turn-out, which included a handful of McDonald's customers. "We have even seen a few of our regulars supporting us."
In Christchurch, more than 30 people braved single digit temperatures to protest outside Linwood McDonald's tonight.
McDonald's worker Maggie Kahunalani, 23, got a big cheer when she walked out to join the protest.
She said things needed to change.
"I have friends who had hours ranging from two hours one week to 30 hours the next," she said.
"People are suffering. You can't live off two hours a week."
In Dunedin, about 20 union members and supporters demonstrated outside McDonald's and Wendy's this afternoon.
Among them was Dunedin City Councillor Aaron Hawkins, who used to work at McDonald's himself.
"The momentum is gathering steam, or we wouldn't see so many businesses giving into public pressure," he said. "We have to keep the pressure on."
However, no staff members went on strike, despite several union members working at the McDonald's store as the protest took place.
Unite Union delegate Callum Turner himself went to work at McDonald's directly after the protest, for the beginning of his 6pm shift. A small crowd also gathered outside McDonald's on Rangitikei St in Palmerston North to protest about lunchtime today.
This morning, McDonald's hit out at the union, saying the strike action was "a stunt" that had nothing to do with the negotiations.
Human resources director Chris Hutton said the company had made an offer earlier this week for more secure hours for workers -- which came after the vote by Unite Union members to go to a strike.
The company later added in a statement: "We're committed to moving away from zero hours contracts and we're committed to bargaining and working through the detail with Unite Union."
Labour employment spokesman Iain Lees-Galloway called on the company to have more respect for its workers.
"If other fast food giants operating in New Zealand are happy not to use these nasty contracts and can guarantee decent work hours, there is no reason why McDonald's can't follow suit."
Prime Minister John Key said the Government was "listening to the concerns that people have" over zero hours contracts and there was a review underway.
Earlier this week, Workplace Relations and Safety Minister Michael Woodhouse announced he wanted to see some of the harshest contracts outlawed.
- Reporting team: Nikki Papatsoumas and Kurt Bayer of NZME. News Service, Simon Collins of the New Zealand Herald, Carla Green of the Otago Daily Times, and Alecia Rousseau of the Manawatu Guardian