Jaap Bosma of the CNV union said the action, under which workers do no more than specified in their contracts, would be followed by cuts in refining volume and eventually complete strikes if no agreement is reached.
“It is definitely not going to remain at just this,” he said.
On Thursday a company statement said: “We regret that we have not yet reached an agreement and that actions may follow.”
The BP refinery in Rotterdam processes about 400,000 barrels of oil annually and is an important supplier of diesel to Northern Europe.
BP’s final offer in talks over a new collective labour agreement under discussion since April had been for a 5% wage increase and one-off bonus of 4,000 euros ($4,000).
Citing Dutch inflation above 15%, workers continue to seek a 6% wage increase, the cash bonus and access to a stock compensation plan representing an additional 3.5% pay increase, Bosma said.
“Safety first!” said the memo seen by Reuters.
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