Cash is not being replaced in some ATMs in Wellington and Auckland while security workers who transport money to the machines hold pay talks.
The industrial action involves 40 workers employed by Australian company Armaguard Currency Management.
The workers replace cash in some ATMs belonging to Westpac and BNZ and transport money for some large retail chains, including Bunnings and Farmers.
The Service and Food Workers Union says the workers have been in negotiations with the company since December to get a guaranteed 40-hour week and a pay increase.
Union spokesperson Jill Ovens says many ATMs will run out of cash if the company does not reach an agreement with the workers soon.
"These guys are wanting to send a message to the employer that they are serious about their negotiations and they wish to have a collective agreement."
Ms Ovens says some ATMs in shopping-malls were serviced on Saturday, but most others have not been filled since before the Easter weekend.