A survey of employers shows the amount of overtime and extra work being done has increased by 27% and 48% of it is unpaid.
The survey of 399 employers by Hays, a recruitment company, shows that where hours increased, 40% of employers said it had risen by up to five hours a week and 42% by 10 hours.
Public Service Association national secretary Brenda Pilott said extra hours are needed in the public service to fill the gaps left by Government cuts.
But Business New Zealand chief executive Phil O'Reilly said most employees are not put under pressure to work more hours.
He said most employees are happy to work extra hours if required, even if that work is unpaid.
Positive sign - minister
Labour Minister Simon Bridges says the amount of extra work being done by employees is positive and reflects what is happening internationally.
Mr Bridges says New Zealanders are known for working hard but globally people are working more flexible hours, such as mothers working from home.
He says he hasn't considered capping the amount of work an employee can do.