Unite Union says SkyCity has broken the law by sacking 200 salaried workers without consultation or discussion.
It said SkyCity's letter of notice stated that the decision had already been made and it was not seeking the employees' views to the extent that it would do under normal circumstances.
Unite Union national secretary Gerard Hehir said the company also did not apply for the government's Covid-19 wage subsidy scheme to save jobs or buy time.
Hehir said the company did not apply to the scheme for salaried workers perhaps because they were generally paid more than waged workers and the company needed to top up more for their pay apart from the government subsidy.
"Hundreds of thousands of businesses with far fewer resources than SkyCity have taken up the subsidies and workers taken pay cuts to save jobs or at least buy some time," he said.
"No-one knows what the situation will be in 10 weeks. If the government is willing to subsidise to allow that then why wouldn't you?"
Hehir said the union had never seen "such a large scale blatant and deliberate breach of the law" around re-structuring and redundancies.
"If SkyCity, a huge corporate with massive resources, can get away with this then it will be utter anarchy. The laws of the land have not been changed. Employers still have to obey the law and their contractual obligations," he said.
"The emergency may mean that consultation times have to be shorter and the dramatic change in business will obviously be a factor in what decisions are justified at the end, but this is complete lawlessness."
Hehir said they would take the company to the Employment Relations Authority if needed.
Included in the 200 redundancies was Julia Liu, a Sea-Unite union leader at the casino. Liu was a food and beverage manager with more than 20 years' service.
"I cannot believe that they are just firing so many workers like myself without any chance to discuss what options there are. After 21 years, it is simply you are fired," Liu said.
She was angry that SkyCity did not apply for the wage subsidy for her job or other salaried managers.
"The subsidy would have more than covered my part-time salary. In fact, it would have provided extra money to subsidise another salaried staff member's wages. They could still have started a redundancy process, but it would have meant that they had 12 weeks to do it properly. How is anyone supposed to find a new job now?"
SkyCity said it did not have any further comment to make at this time, but referred RNZ to a statement it put out earlier, which said that changes were being implemented to minimise the impact of Covid-19.
"These changes include significantly reducing capital expenditure and minimising operating costs, including the immediate restructure of the SkyCity management team and salaried employee base," it said.
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