The Medical Laboratory Workers Union says skilled staff will leave the sector because of job uncertainty created by constantly changing contract arrangements.
Canterbury Health Laboratories in Christchurch has lost a contract to provide specialist medical testing for the MidCentral District Health Board.
The work is being transferred to a provider in Auckland, LabPlus.
Union president Stewart Smith says some of the work going to Auckland will have to be returned to Christchurch anyway because it can not be done anywhere else.
He says that shows a national strategy is needed to better coordinate the provision of laboratory services.
Mr Smith says staff are already leaving the sector because they are disheartened by the fickle way in which contracts are awarded.