Women working in transport industries are taking medication to dehydrate themselves because they can't access a toilet at work, according to the Rail & Maritime Transport Union (RMTU).
At a recent forum for female union members, workers shared horror stories about the facilities available to them in the historically male-dominated industries, particularly rail.
Male urinals can be found in women's bathrooms, and in some workplaces there is no female bathroom at all.
In one South Island railway workplace, two women discovered that they were expected to share the men's toilet and shower facilities.
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When the RMTU complained on the women's behalf, the initial response was to offer only a "sanitary bin" for female staff.
In a railway mechanical depot, the women's wash facility is in a separate location to the changing room, meaning women have to run the gauntlet in a towel from their workplace shower to the changing room.
Union health and safety organiser Karen Fletcher said it was not acceptable for employers to expect women to use men's toilets - or for anyone working in the field to have to go behind a bush.
"Some women have said that they either dehydrate themselves by not drinking anything before they go to work and the night before, so they won't have to make too many stops during the day when they're working remotely," she said.
"Other women have said that they actually take medication that dehydrates you and stops the need for going to the toilet, which is of course a really serious health and safety issue."
Fletcher said if employers were serious about encouraging more women to work in blue collar industries, they needed to make women welcome by providing adequate toilet and wash facilities.
"Expecting people to just pop a squat in the bushes while they're working on a railway track is not okay. It's time to do something about it," she said.
RMTU national secretary Wayne Butson said women have been holding on far too long in their wait for safe and secure bathroom access.
"We should all be able to take for granted our right to go to the toilet when we need to. Unfortunately, too many employers do not provide suitable bathroom facilities for their staff," he said.