The national Blood Service says it has no additional funding to match staff pay to that of their Health New Zealand counterparts.
Nearly 300 blood service lab workers have walked off the job on Tuesday, the latest in a series of actions calling for pay parity.
Blood Service chief executive Sam Cliffe said it budgeted for increased pay after the negotiations between unions and Te Whatu Ora, but the new rates are more substantial than anticipated.
The Blood Service gets no government funding for pay equity settlements, she said in a statement.
"We are committed to matching the agreed Te Whatu Ora pay rates and we're having ongoing discussions with the Ministry of Health as we seek to reach a satisfactory resolution, while operating in an environment of financial restraint," Cliffe said.
Apex union lab workers president Bryan Raill told Morning Report negotiations had been ongoing for seven months.
Blood service workers strike over pay
"It's all on the Blood Service to resolve this.
"The impact on hospitals will be there'll be some elective surgery deferred, and the public have a right to be annoyed at New Zealand Blood Service for not resolving this already."
Raill said the Blood Service had agreed in principal to pay parity, and had started paying its nurses the same as those employed by Te Whatu Ora.
"But they're just not doing it for their lab staff... New Zealand Blood Service just has to come to the party."