He said the members are seeking the same pay rates care and support workers receive as a result of the equal pay settlement.
"It's the same kind of work. They are entrusted with the care of other people's children, but their work is undervalued."
He said the union had not been informed of arrangements to cover the matrons overnight, but did confirm the majority are union members, therefore striking.
"If the school principal or the chair of the board is going to be sleeping in tonight and finding out what the work is like, then I think that is a really good thing."
The matrons' spokeswoman Tracey Whittington says they are struggling without secure hours.
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"We feel undervalued and the pay rate doesn't reflect our responsibilities or the unsociable hours we work.
"We all work shifts, including weekends."
She said she was contracted to work 72 hours a fortnight, but has not been paid for that many hours since September.
"That makes my life a struggle. I have a mortgage to pay. Most of us are sole income earners so this is important to us."
She described being a matron is being like a second mother to the students, with up to 160 boarders at any one time, ranging from ages 11-18.
"We know the girls' personalities, you can pick out when a girl is having a bad day, you are just there to support them, ask them if they are okay."
"It's the day-to-day care, getting them ready for prep, for dinner, getting them ready for bed."
She said the matrons did not take striking lightly.
"It has taken two years for us to get to this point.
"We don't like upsetting the girls' routine, because we spend most of the year trying to get them into a good routine."
The members say if pay is averaged out over the year, they are barely earning above the minimum wage.
One matron Julia Alexander, says she is lucky to have a supportive partner who receives superannuation.
"A lot of these women don't have that support and it's very hard for them."
The members have agreed to return to work on Thursday, in order to support students who begin NCEA exams on Friday, but said if there is no progress they are prepared to strike at a later date.
According to the Iona College website, boarders pay $3320 per term to attend the school, equalling $13,280 for a year's tuition.