More miners are today expected to join an indefinite strike in support of 100 locked-out workers at Waikato's Rotowaro mine.

The Rotowaro open-cast workers were locked out on October 27, after beginning go-slow industrial action in response to failed contract negotiations with Solid Energy and its contractors.

About 160 Huntly East underground mine workers walked out in support the following day and yesterday 400 workers at the West Coast Stockton open-cast mine also walked off the job indefinitely.

Workers at Spring Creek mine, near Greymouth, took solidarity action for 24 hours last Friday and were due to meet later today to discuss further strike action.

Engineering, Printing and Manufacturing Union (EPMU) spokesman Ged O'Connell said it was likely the 160 Spring Creek miners would join the strike.

All four mines are part of a multi-employer collective agreement (Meca) with Solid Energy and its contractors, which has not been ratified despite expiring months ago.

Mr O'Connell said negotiations had reached a stalemate.

"This is a battle that the miners have had with Solid Energy for some years now, in terms of how its contractors deal with its employees," Mr O'Connell said.

"Often there's an arrangement made between Solid Energy and its contractors without involving the employees, and when it gets to them we find it doesn't fit, so then there's a breakdown with the contractor."

Mr O'Connell said in the case of the Rotowaro mine, the contractor was insisting on new rosters which the workers were unhappy with.

While workers at the three other mines had stopped work in support of the Rotowaro workers, Mr O'Connell said they were also suffering from the same problems with contractors and that Solid Energy needed to address the issue.

"When they make arrangements with contractors that affect their employees without consultation with the employees it's foolhardy," Mr O'Connell said.

"You can't screw your contractor, then have the contractor screw his employees and say `oh, it's nothing to do with me", it's their problem."

Union delegates for the Rotowaro workers would also enter discussions with their employers today to discuss possible mediation.

A Solid Energy spokeswoman said the company would comment on the industrial situation later today.