"An estimated 30,000 women working in aged care have been underpaid and undervalued for too long."
NZ Nurses Organisation aged care industrial adviser David Wait said the cases were just the beginning.
"Over the next year we expect thousands of caregivers in be involved in legal action demanding equal pay.
"The work caregivers and health care assistants do for our vulnerable elderly is incredibly important in our society.
"We will all lose if we don't recognise the value of the work with a fair and decent pay rate that's equal to what would be paid if the sector were male-dominated."
Mr Wait said a big part of achieving equal pay was for the Government to step up and fund residential aged care providers properly.
"We're hoping this legal action will encourage the Government to do the right thing."
Mr Wait said some 400 applications to the ERA had been filed on behalf of hundreds of caregivers at homes around the country - about 200 per union.
The applications were effectively the same as those filed by the SFWU on behalf Lower Hutt caregiver Kristine Bartlett, which resulted in a landmark ruling paving the way for gender pay equality.
In August, the Employment Court found in favour of Ms Bartlett, who argued the $14.32 an hour she was paid by Terranova Homes was a result of gender discrimination under the Equal Pay Act.
The court did not challenge the fact that Terranova paid its four male caregivers at the same rate as its 106 female caregivers, but it ruled that the four male caregivers were not a big enough comparator group to establish whether the low pay rates for the largely-female workforce were discriminatory.
Terranova Homes is appealing the decision, with the case due to be heard in the Court of Appeal in February.
Mr Wait said the unions had asked the ERA to wait for the outcome of the appeal before hearing the new cases.
He anticipated the cases would be heard together, with thousands more workers expected to join the action next year.
Mr Wait said it was not known how much a successful outcome could end up costing the aged care companies, as the appeal would have to be decided before a wage rate could be set.
But a 2010 report by the Human Rights Commission found the cost of paying caregivers the same as DHB-employed health care assistants would be $139 million to $141 million a year.
Mr Wait said the caregivers were significantly underpaid.
"I wouldn't be surprised if the result of Kristine's case is actually that these people should be paid more than health care assistants with the district health board."
Read more: Herald's 'Inside our rest homes' series