The Medical Laboratory Workers Union says some lab employees in Canterbury still face considerable uncertainty.
A new partnership was launched on Sunday between Canterbury District Health Board lab and Southern Community Laboratories.
A third firm, Medlab South, lost its share of the work, but has been taken over by the owner of SCL, Healthscope.
Medlab South personnel now work for SCL and generally have been promised roles in the new partnership or in the wider health system.
But union president Stewart Smith says sickness in particular could provide problems.