The Defence Force denies it tried to stop civilian staff taking part in a strike for better pay, but the Public Service Association (PSA) says it acted unlawfully.
The PSA, which represents 600 civilian staff in administration, security, and catering, scheduled strike action for Palmerston North today, Wellington tomorrow and in Auckland next week.
The union's national secretary, Glenn Barclay, said some civilian staff had not had pay rises in three years, and the Defence Force had failed to negotiate their pay as part of a new collective employment agreement.
The workers planned to demonstrate with signs and flyers, and some staff in Auckland would not answer phone calls or emails.
In a letter sent to staff, the Defence Force said all employees were required to perform their regular duties, and those who failed to do so would be treated as being on strike.
The strike in Palmerston North went ahead today, but the PSA said it believed some staff stayed on the job because of the letter.
PSA spokesperson Nick Kelly was at the two-hour event, and said the letter was likely to have spooked some members.
"Unfortunately, [the Defence Force] has been using tactics of intimidation and has sent a letter to our members trying to pressure them not to attend. When an employer pulls those sort of tactics, which we don't consider lawful, we wouldn't be too surprised if the number of people are a bit concerned about attending."
Union lawyer Peter Cranney has written to the Defence Force, saying the letter its members received was "unacceptable".
He said the right to strike lawfully was a fundamental human right, and that was expressed in the Employment Relations Act.
Mr Cranney said the Defence Force indicated it planned to give the names of non-strikers to the Ministry of Business, Innovation and Employment, which was not a requirement.
"These types of intimidatory statements have no place in New Zealand society.
"While there is an obligation to inform MBIE of the existence of a strike and of the number of strikers, you [Defence Force] are neither entitled nor required to identify strikers or non-strikers by name," the letter said.
The Defence Force said the letter did not tell staff they were not allowed to strike, and it only asked non-striking staff to continue to work. It said no names were passed on to MBIE and negotiations for better pay were continuing.