Unite said Ineos was behaving "recklessly" in rejecting its request to use Acas.
The site directly employs 800 people and staff have launched a work to rule and overtime ban in a row over the treatment of Stephen Deans, Unite convener. The company is conducting an internal investigation into Mr Deans, who has worked at the plant for 24 years.
The union has warned it has not ruled out strikes.
Unite regional secretary Pat Rafferty said: "It is our view Ineos is using Stephen Deans, who is an innocent man, and the country's energy supplies as pawns in some twisted industrial game.
"The company's inaction will force the union into industrial action that would inevitably put the nation's fuel supply at risk.
"This latest move by Ineos to refuse the opportunity to use the conciliation service Acas to try to resolve this dispute is utterly baffling."
Ineos has warned the petrochemical site will close in 2017 without fresh investment and reductions in costs.
An Ineos spokesman said: "Unite only wanted to go to Acas over the Stephen Deans issue, not the survival plan.
"There is an investigation going on into Stephen Deans that will be completed by October 18. Until the investigation is concluded, we do not know all the facts. Going to Acas without the facts is a pointless exercise."