More than 800 coalminers are taking industrial action after multi-employer collective agreement talks broke down.
The action, which began on Monday, included a nationwide overtime ban and a series of spontaneous rolling stoppages aimed at disrupting production at 11 mines covered by the collective agreement.
Engineering, Printing andManufacturing Union acting national secretary Ged O'Connell said the agreement covered Solid Energy and seven or eight of its contractors.
The strike action started on Wednesday with West Coast miners for several hours walking off the job at Solid Energy's Spring Creek (Greymouth), Terrace (Reefton), and Stockton (Westport) mines.
Last night, Waikato miners refused to work at the East Mine in Huntly.
The union had been trying to negotiate a deal for the past two months, and miners were willing to fight for their fair share, Mr O'Connell said.
The union is seeking a pay rise of between 5 per cent and 5.5 per cent.
Solid Energy had responded with an offer around 4 per cent, he said.
The company's board appeared to come to the table with a pre-set remuneration policy, he said.
"These guys do hard and dirty work every day in an industry that's making very healthy profits.
"All they want is a pay rise that reflects this, but the companies are refusing to budge."
The difficulties had been compounded by Solid Energy's refusal to negotiate alongside the contractors, so the union had to meet them separately.
The union viewed this as an attempt to thwart the collective agreement.
Mr O'Connell said talks with some contractors were scheduled for next Wednesday and the rolling action was likely to continue until then.
