Unite's Len MCluskey has told Grangemouth owner Ineos that the union will embrace the rescue plan.
Following emergency talks with Ineos management this morning, McCluskey said that Unite "was not going to allow this plant to close down".
On BBC News 24 he said that they will not let 800 jobs go and see Grangemouth become a ghost town.
McCluskey didn't detail what the union have agreed to, but it appears Unite has now conceded that workers must accept the pay freeze and pension cuts that had been rebuffed.
The union's change of mind comes after discussions were at a standstill yesterday, following a staff vote on the plant's Survival Plan that saw a 50/50 split. But by late evening Unite seemed poised to co-operate with Ineos.
BBC coverage of McCluskey speaking at Grangemouth can be seen on their website.