One third of the 1.4 million fulltime workers in New Zealand work 50 hours a week or more, according to the Department of Labour.
The department says a study using data from the 2006 census reveals a high number of employees are working excessive hours, which it says affects their families and the community.
It says long working hours can also have a negative impact on health and safety in the workplace and reduce productivity.
The department says the study highlights the importance of negotiating flexible working arrangements.
Information revealed by the census data will be used target future employment initiatives towards greater work-life balance.