The National Distribution Union says it shares the Fire Service's concerns that building owners and businesses could be putting cleaners' lives at risk.
This comes after cleaning staff were trapped inside a Masterton supermarket when arsonists set fire to materials stacked against supermarket walls on November 4.
The cleaners escaped unharmed when the Fire Service arrived.
The National Secretary for the National Distribution Union, Laila Harre, says there have been many situations where cleaners would have been at risk had there been a fire.
She says exits are often not accessible in supermarkets due to the stacking of pallets, and delivered goods blocking fire exits.
Ms Harre says cleaners are also more susceptible to fire hazards because they work outside regular hours.
The Fire Service's safety integration manager, Gary Talbot, says it is a breach of safety laws to store materials that may be a fire hazard near or inside a building. He says it is especially important over the holiday period that people who enter buildings have an escape route if they need it.
