The Rail and Maritime Workers Union is using World Toilet Day to highlight a lack of lavatories for female workers.
The union says women have shared stories at a recent forum of having to use men's toilets with urinals and lack of access to changing rooms.
RMTU health and safety organiser Karen Fletcher says it's not what you expect in New Zealand.
She says a lot of workers limit their fluid intake, even from the night before.
"We've even heard cases of people taking medication, such as hay-fever medication which dehydrates you, so they don't have to go to the toilet."
Fletcher says it's incredible women and men have put up with the issue for so long.
She says if employers are serious about encouraging more women in blue collar industries, they need to make them feel welcome with adequate facilities.
KiwiRail Chief Operating Officer Todd Moyle says they're halfway through upgrades for all KiwiRail sites.
He says they've completed facilities for women at 10 sites over the past year, with six more to be finished in the next few months.
Moyle says they're also working on providing options for travelling staff and isolated sites not accessible by road.