reason for industrial action

Any ideas on the reason for the industrial action at Smoky Hills?

One thought that comes to mind is that PLAA are driving Redpath hard to incraese production and show progress at meeting targets.

I do not really see that this can be a pay issue as Redpath would have a remuneration plan across all its projects so if this were the case we would probably see much wider strike action.

Safety grounds would be the most concerning issue, but could Redpath really threaten to terminate their employment if they do not return to work?

All views would be appreciated.

BR
Max