The arrangement worked like clockwork until a new boss arrived and put an end to the flexible hours at Liverpool Hospital in Sydney's south-west, where the twins Craig and Cameron both work as painters.

Their wives and the NSW Health Minister are now asking why the hospital has fought for two years the brothers' attempt to maintain their family-friendly hours.

Michelle Zammit said her husband Cameron had been working from 6am until 2.30pm for eight years without complaints from the hospital, allowing him to pick up their children from school at 3pm.

The hospital's sudden decision to force him to start work an hour later was stressful and inconvenient because they were both working and paying their mortgage.

"We have to share the load," she said.

"I think if he was a woman it might be looked at a little bit differently.

"I don't think it should be up to the woman to take on the majority of the load."

Labor's spokesman on industrial relations Adam Searle said a NSW Industrial Relations Commission decision to give the South Western Sydney Local Health District the final say on the men's working hours was "unjust", "old-fashioned" and showed the "law is not working properly". The Zammits will appeal the decision next month.

"The employer could not quantify the financial cost claimed or point to any real operational disadvantage of continuing the long-standing flexible work hours," Mr Searle said. "But the negative impact of ending the arrangement on these families was clear."

Mr Searle said Labor would focus on doing more to help families achieve work and family life balance.

"If men are not permitted flexibility in working hours, it will impair women's ability to participate in the workforce," Mr Searle said.

"Why should parenting responsibilities fall only on women? Why should male workers not be allowed to work flexibly to participate more fully in family life?"

NSW Health Minister Brad Hazzard told Fairfax Media he was looking into why the men had been stopped from continuing their flexible work arrangements.

"Flexibility in the workplace anywhere should be a desirable outcome provided the workplace can still work, and for taxpayers it has to work well," he said.

"What the South Western Sydney Local Health District are telling me is it does not work well for the rest of the workforce who are delivering for patients in the hospital.

"At this point I have to accept that, but I am going to inquire as to the ages of the people's children to get a better understanding of the situation."

Paul Connell from the CFMEU, which represents the men, has called on hospital management to resolve the long-running issue to avoid wasting more taxpayers' money on legal costs.

"I am appalled at the amount of taxpayers' money being spent arguing over one hour when the health system is incredibly underfunded," Mr Connell said.

"This contradicts what the NSW government has said about wanting public sector employees to have more flexible working conditions by 2019 and what Liverpool Hospital has said about wanting its employees to have a better work/life balance."

NSW Health said it is "committed to providing flexible work arrangements to support staff in balancing their work roles with personal obligations, where appropriate".

"However, any decisions about flexible working arrangements must be consistent with the imperative to maintain appropriate levels of service to patients and clients of NSW Health."

A Liverpool Hospital spokesman said: "Flexible work practices are an important work option and the decision making process must take into consideration the needs of the business or service as well as those of the applicant."