Shell is embroiled in a pay dispute with workers at its Pernis oil refinery in the Netherlands.
A spokesman for the FNV union told Reuters that employees were ready to close half of the on December 7 because Shell only wants to give them a raise of 1%.
Workers are believed to be holding out for a 1.5% pay rise.
A Shell spokeswoman was cited as saying: “The unions indicated that they intend to continue activities [as early as next Wednesday]. Should this be the case, they will have a financial consequence. We are confident that we are going to reach a solution.”