Emergency Department doctors are accusing Health New Zealand of failing to pay a shift allowance agreed 10 months ago in their previous collective contract.
Mediation is underway, after the Association of Salaried Medical Specialists took their case to the Employment Relations Authority.
The union's executive director, Sarah Dalton, said the shift allowance of 20 percent (on top of the base salary increase) was in recognition of the "particularly gruelling" nature of shift work for emergency department doctors.
"That's not to say that other specialities don't have onerous on-call rosters, but it's much more variable in ED.
"And it was also to specifically focus on the massive increase in acute presentations that EDs are experiencing and the significant staffing gaps that a number of them are trying to manage."
Health New Zealand had been slow to pay out agreed increases to several groups of health workers, which had been "frustrating", Dalton said.
"There were delays in payment of agreed increases right across the board, and some groups were waiting upwards of six months to see those pay increases."
RNZ has asked Health New Zealand for its response.
The ASMS settled its pay negotiations with Health NZ on 1 December, 2023, following months of bargaining and unprecedented strike action.
At the time, the union said the weighted average pay rise of 5.73 percent across all salary bands was the first time in three years that its members had not had "a pay cut in real terms".
Te Whatu Ora's Chief People Officer Andrew Slater said the agency was still engaging in a formal process with the union, "it would be inappropriate to provide any public comment while that process is underway".