Part-time high school teachers have become the latest group to lodge an equal pay claim, as the effects of this week's 20 per cent-plus pay rise for caregivers roll out to other female-dominated groups.

The Post Primary Teachers Association (PPTA) will lodge a claim in the Employment Relations Authority today (Monday July 3) to trigger an equal pay claim for 3380 part-time teachers - 72.5 per cent of them female.

The claim is the third in the education sector, and at least the fifth claim lodged across all female-dominated groups, since the Government agreed to pay 55,000 caregivers wage increases of between 15 and 50 per cent from July 1.

The primary teachers' union, the NZ Educational Institute, also signalled a planned claim last week for 24,000 early childhood teachers, and other unions say pay equity claims are being raised in all wage talks for female-dominated sectors as collective agreements come up for renewal.

But the claim for part-time teachers is unusual because it is not about hourly pay rates.

Instead, part-timers want to be paid for time spent preparing lessons and marking on the same basis as fulltime teachers, who won one hour of paid non-contact time for every four hours in the classroom through a series of negotiations from 2002 to 2008.

That would mean an effective 25 per cent pay rise for part-timers who currently get no paid non-contact time - about one-third of all part-timers.

The other two-thirds get some paid non-contact time, varying from school to school, but only 15 per cent get the same one-hour-for-four ratio that fulltime teachers get.

Leanne Donovan, a food technology and social science teacher at Thames High School, had to take on a second job at nights because she gets no paid non-contact time, although she does get an 11 per cent pay loading which partly compensates.

"I worked at a pub on Saturday from 11am till closing for five or six years. Then I used to work all day on a Friday and go straight to the pub till 2 or 3 in the morning," she said.

She teaches for 16.6 hours a week, just 3.4 hours short of the classroom hours of a fulltime teacher.

She has requested a fulltime job for 10 years but has not been granted one.

"I worked fulltime for two years, I was just filling in for someone," she said.

"In those years I had five hours' non-contact time. It was a huge difference. You had a lot of time to get all your planning done, you were there for the meetings. It was just amazing, the difference."

Pam Foyle teaches 19 hours a week at Tauranga Girls' College but gets only one hour of paid non-contact time - four hours less than she would get if she had one more hour of classroom time.

She has taught at the school for 20 years, starting on a fixed-term contract and eventually teaching fulltime for five years, but has been unable to get one extra hour's class time in recent years.

"When I started at the school I was a single parent and wanted a job, so you don't make waves," she said.

"You are in quite a vulnerable position when you are not permanent, so you just take what you can get and hope it will evolve."

The PPTA said in a letter to Ministry of Education head Iona Holsted that the ministry had agreed in 2008 that non-contact time for part-time teachers was a pay equity issue.

But the ministry's deputy secretary Ellen MacGregor-Reid told the New Zealand Herald that the ministry now does not think the issue should be considered under pay equity principles.

Women also make up 57 per cent of fulltime secondary teachers, although the imbalance is less than their 72.5 per cent of part-timers.

The ministry said all part-timers received the 11 per cent pay loading "to recognise their participation in activities of the school which are outside of classroom teaching".

It said secondary teachers earn an average of $77,474 a year including salary and allowances.

55,000 workers in aged and disability care received the first tranche of pay rises of between 15 and 50 per cent on July 1.

Claims lodged in 2015 for social workers employed by Child, Youth and Family (now Oranga Tamariki), are now being discussed in a working group.

Claims lodged for 300 Ministry of Education employees working with young children with complex needs, is in negotiation.

15,000 teacher aides, librarians and other support staff reached an agreement with the Ministry of Education on June 16 to negotiate a pay equity claim.