About 100 Otago Department of Conservation staff and 1500 throughout the country will take industrial action from tomorrow over pay.
Members of the Public Service Association (PSA), which represents Doc, are unhappy with what they describe as an ''insulting'' pay increase offer of 0.4% from the department.
Otago PSA workplace delegate and Doc technical adviser Bruce McKinlay said staff were frustrated it had come to this.
''[The] bargaining is becoming fractious,'' Mr McKinlay said.
''We've gone through a long period of restructuring [and] staff would actually like to have a collective agreement [finalised] so that [they] can get on with work.
''Some of the proposals on the table just aren't acceptable.''
Doc staff would ''work to rule'' during the month-long period of industrial action.
It meant they would work only the hours they were paid, would take breaks they were entitled to and would not answer phone calls or emails outside work hours.
They would also not be available to be on call or on standby.
Mr McKinlay said some staff had missed out on ''where they wanted to go'' when restructuring took place in 2013 and the collective agreement, including pay negotiations, had added to the frustration.
Staff felt they were not taken seriously by their employer, he said.
''We hope that we can get back around the table and have a proper conversation.''
PSA media adviser Asher Goldman said they had been in negotiations over the collective agreement since August and the offer was a ''joke''.
''Doc staff put in huge hours outside the normal hours. They do their jobs because they are incredibly passionate. They're stretched and overworked,'' Mr Goldman said.
The action was about the message it sent and staff were left with no choice, he said.
The industrial action could have quite a significant impact for the public and Mr Goldman wanted the department to come back with ''something not so insulting''.
PSA had asked for a 3% pay increase.
A Department of Conservation spokesman said an offer was put forward for PSA members to consider and negotiations were continuing.
