"Our members at Justice work hard to keep the court system going. Many of them are women, and they do crucial jobs such as court registry officers, court reporters, victim advisors and Family Court co-ordinators," PSA national secretary Erin Polaczuk said
"They deserve to be properly valued for the work they do in making sure the justice system runs smoothly and fairly."
A female employee at the Ministry is paid on average 15 per cent less than a male worker, the PSA said. It is a larger gender pay gap than the average public sector department of 12 per cent.
The Government requires all public service employers to end the gender pay imbalance by 2020.
"The PSA believes the Ministry does not properly value some female-dominated roles - and our efforts to strike a deal to reduce this pay gap and have staff properly valued have so far come to nothing," Polaczuk said.
"These are not highly-paid workers. Last year, Justice had the third-lowest average salary in the public sector, and we believe they are slipping back even further."
Ministry of Justice chief executive Andrew Bridgman said his ministry remained open and committed to continued negotiations.
"We have offered a 5 per cent increase over two years, which is consistent with agreements reached by other government agencies. The PSA have asked for more than 13 per cent over the same period."