The Unite union said it was given 665 forms by last night's 6pm deadline rejecting the offer of a pay freeze and changes to pension conditions from the 1350-strong workforce.
Ineos, which had threatened to close the plant for good unless workers agreed to a survival plan, would only say a shareholders' meeting planned for today would discuss the matter.
But while Unite hailed the rejection by 65% of its Grangemouth membership of the company's demands to sign up to the proposals, there are fears over the next move by Ineos and its chairman and founder Jim Ratcliffe.
The rejection has sparked renewed calls for political intervention by both the Scottish Government and the Coalition Government, with sources claiming the deadlock could be broken by stakeholders such as PetroChina or BP. PetroChina owns a substantial percentage of Scotland's biggest oil refinery.
A senior union source said: "There's a nervousness about what happens now. Ratcliffe won't mess about. He calls the shots, not shareholders. The knot's tightening but is he going to sack 50% of the workforce with a view to more?
"The result shows this isn't a handful of mavericks opposing these terms. What this needs is huge political intervention over what is a corporate shutdown, not a strike."
The refinery, which has an annual capacity of 10 million tonnes, provides most of the fuel in Scotland, Northern England and Northern Ireland.
Ineos has warned the plant, which remains shut down despite the planned strike by Unite members being called off, is losing £10 million-a-month and would close in 2017 without new investment and changes to workers' terms and conditions. It has offered those who supported the survival plan a transitional payment of up to £15,000.
But Unite has accused the company of giving workers an ultimatum of accepting worse pay and conditions or losing their jobs.
The two sides have been embroiled in a bitter dispute for weeks, initially over the treatment of Unite convener Stephen Deans, who was involved in the row over a selection of a Labour candidate in Falkirk, where he chairs the constituency party.
He was suspended, then reinstated, and is facing an internal investigation, which is due to report on Friday, with speculation he could be a casualty of Unite's rejection of the terms.
Mr Ratcliffe said at the weekend that the fate of the plant rested with its staff.
He said: "This is not a bluff. The clock is ticking. Grangemouth could have a future but that is absolutely in the hands of the workers. If we go down the wrong road, then I'm afraid this story will not have a happy ending."
Urging the company to return to talks at the conciliation service Acas, Pat Rafferty, Unite's Scottish secretary said: "This resounding rejection of the company's cynical blackmail sends a clear message to the company.
"The people of Grangemouth and Scotland will be expecting Jim Ratcliffe and the Ineos shareholders to now take heed. Do the right thing tomorrow, drop the threats to the workforce, fire up the plant and get around the table at Acas.
"This workforce has said that they want to secure a future for Grange-mouth, free from fear, based on negotiation not confrontation.
"With Ineos making £2 billion in profits last year, people don't think that their claims of financial distress stack up."
Meanwhile, Mr Deans laughed off suggestions that he had signed up to the company deal and accused Ineos of exaggerating the numbers of those who had. He had been the subject of rumours that he may have broken ranks to accept the compulsory terms.
He said: "That is absolutely, horrendously wrong. I can't describe how ridiculous that is without using foul and abusive language. But what is true is that we have been flooded with forms at the Unite office."
A spokesman for Prime Minister David Cameron said: "There is a responsibility on all sides and that's why it is important that they continue to try to find an agreement that ensures a sustainable future for the facility."
First Minister Alex Salmond repeated earlier calls he made during the SNP conference in Perth for Ineos to "fire up the plant" and for Unite to commit to a "no strike, without strings, guarantee".