Workers at the Ineos site start an overtime ban and work to rule today, in support of a Unite convenor.
Stevie Deans was suspended, then reinstated, by the company over allegations linked to his involvement in the bitter row over the selection of a Labour candidate in Falkirk, where he is chairman of the local constituency party.
Unite accused Ineos of trying to "provoke" a strike, which it warned would be "hugely damaging" to the UK economy.
For its part, Ineos denies victimisation and has warned repeatedly that job cuts are expected at the plant as a result of market pressures.
Yesterday, the company said one of its subsidiaries, Hull-based VAM, was to close, with the loss of 18 jobs.
It blamed low-cost imports and a "hostile" trading environment, as well as the "high cost" of products from Grangemouth.
Unite Scottish Secretary Pat Rafferty said: "The company is holding Stevie Deans hostage, and playing Russian roulette with fuel supplies.
"The changes being proposed are completely unpalatable to us and we feel we are being pushed into taking strike action."
Scotland's Finance Secretary John Swinney, said: "We are currently in active discussions with the unions and Ineos in order to resolve the current situation and offer support for their future plans. We will continue those active discussions in the days ahead."