Spark has given around 1900 staff one week to sign a new employment contract or leave the company.
Spark spokesperson Lucy Fullarton confirmed to the Herald that the new contracts had been handed out to staff in the last few days.
"We have been discussing this with our people for several months, including formal consultation over recent weeks with affected people on proposed changes to their roles," Fullarton said.
"The new contracts were shared with affected staff in the past few days. As per our standard process, we are giving employees five working days to consider their new contract."
The move comes after the Auckland-based telco said last month that it would bring forward its restructuring programme, dubbed "Quantum Programme", to transform the country's biggest telecommunications company into the operator with the lowest costs.