Popata said the decision to strike came about during the members' collective agreement bargaining.
"Their bottom line wasn't met. They've said 'this is what we believe we're worth - 2.5 per cent is not much' but InfraCore said it couldn't be met, they get a limited amount from the council.
"The only thing our members have is their labour so they plan to withdraw it."
Popata said a meeting would be held to discuss the strike and Infracore would be given an official notice of the strike action.
He said essential services would be covered during the strike.
First Union's Phil Graham said details of the strike could not be revealed at this stage.
The action involving InfraCore staff is unrelated to issues with the outsourcing of the Rotorua Aquatic Centre.
Last month it was revealed 27 staff were asked to reduce their pay to market rates to allow the company to be more competitive, grow and pay other staff members more.
InfraCore, which employs the city's parks, water, civil works and nursery staff, is in pay negotiations with its 150 staff.
Hammond previously told the Rotorua Daily Post the staff's pay rates were "out of kilter" with market rates and if something wasn't done to address them the "wheels will come off" the business.
Rotorua Lakes Council set up InfraCore three years ago, replacing Castlecorp. It's owned by the council but is run as a separate business, holding contracts with the council.
InfraCore operates from a Vaughan Rd depot and Queens Dr nursery and maintains Rotorua's gardens, parks, reserves and cemeteries as well as the city's water and wastewater networks and land drainage systems.