About 950 coal miners throughout New Zealand are now on strike after workers at Spring Creek mine near Greymouth walked off the job on Wednesday night.
Workers are striking after a breakdown in contract negotiations with state-owned mining company Solid Energy.
The industrial action began when 180 miners at Rotowaro Opencast mine walked off the job last week, followed by colleagues at Huntly East Underground mine in Waikato, and Stockton and Spring Creek on the West Coast.
Solid Energy says mediated talks on Wednesday with the Engineering, Printing and Manufacturing Union and the contractor HWE Mining failed to reach an agreement to resume negotiations.
Solid Energy says it cannot resume bargaining while industrial action continues and is calling on the Engineering Printing and Manufacturing Union to stop the industrial action.