The trade union, Unite, said it plans to invoke its mandated overtime ban and a work-to-rule that is scheduled to begin by Monday at the Grangemouth site near Falkirk as the deadlock with operators Ineos continued.
Strike action has not been ruled out, the union said, over the alleged ill-treatment of a suspended union representative and the growing use of agency workers.
Ineos denies victimisation and added that job cuts are expected at the plant as a result of market pressures as it called for government grant backing to help protect 800 workers whose livelihoods are at stake.
Pat Rafferty of Unite, said yesterday negotiations would continue.
He said: "We are trying our level best to try and get these issues resolved without the need to escalate further industrial action."
A spokesman for Ineos said: "This week we launched a survival plan for the Grangemouth site, so at this critical time we are extremely disappointed that the threat of industrial action remains.
"We urge the union to join us in fighting for the long term future of the site."
Unite said members are in dispute with Ineos partly over the treatment of union official and Ineos employee Stephen Deans.
The company launched an investigation into Mr Deans, who is also chairman of the Falkirk Constituency Labour Party, after he was caught up in the controversy surrounding the selection process for a candidate for disgraced MP Eric Joyce's seat.