Respondents cited anxiety, unmanageable workloads, the subject matter of their work, and feelings of not being valued as reasons for stress.
"Concerningly, bullying by senior staff was frequently mentioned as a cause of poor mental health," the report said.
ALWU co-president Tess Upperton said mental health issues were a summary of the other challenges staff were dealing with.
"When you've got excessive working hours, you're not getting overtime, you're not getting time off, you don't have a particularly diverse or supportive workplace, then of course these all play into how you are feeling about your work."
The ALWU said it was "saddened" to see the latest report continued to reflect significant issues of mental health in the legal profession.
It said more needed to be done to alleviate stress and mental health must be prioritised over profits.
Upperton said the staff who were able to put up with these conditions would remain in the industry while those who could not would eventually leave.
That was how you get a particular face to an industry, she said.
Lack of paid overtime
The report found that people in the legal sector were working an extra 4.69 hours per week for no extra pay.
The situation was worse at large private law firms, with staff reportedly working close to an extra day a week.
Only 3 percent of respondents said they had been paid overtime.
Upperton said the lack of overtime was particularly "galling" given that the industry relied on hourly billings.
This meant employers were directly benefiting from every unpaid hour an employee worked.
"We really see overtime as a key tool, not just to make sure people are being paid for their labour, but to also protect against these mental health effects we're seeing in the industry."
Upperton said if overwork had a financial cost to an employer then overtime hours might decrease.
Lack of progress on female partners
The report found there was a minimal change in the percentage of female partners at private law firms in New Zealand.
Just over 33 per cent of partners at the country's largest law firms were women.
Upperton said this was despite 75 per cent of law school graduates identifying as female.
But she added this was just one measure of equality in the legal sector.
"Having women at the top does not automatically translate into wonderful [careers] for women or other groups as well."
The report indicated that female respondents also tended to be less satisfied with the hours they worked and the culture of their workplaces, when compared with their male counterparts.
Women also reported feeling less valued in their work and had a higher incidence of poor mental health.
Upperton said a priority for the ALWU over the next year would be to collect more data on disabled, non-binary, Māori and Pasifika people, all of whom were not well represented in the sector.
Salary issues
A bright spot in the report was that the median salaries for those entering the industry had increased by 14 per cent on the previous year.
However, pay for entry level legal workers in the public sector had fallen 1 per cent.
Upperton said the findings were "somewhat surprising" because traditionally the public sector was regarded as a more comfortable place for workers to start their careers.
"I think a big cause of that is the public sector pay guidance that effectively restricts union and an individual's ability to negotiate salary increases or increases that reflect inflation."
She said it was difficult to say if the pay freeze would result in public sector lawyers leaving for private firms because they tended to be happier in their work, less affected by long hours and more likely to recommend their work hours.
"I think it goes both ways, but it is a new shift that we are seeing, and we could start to see some flows because of it."
A link to the report can be found here.
