Workers at the BP Plc oil refinery in Rotterdam are threatening to strike if their pay demands in a new collective bargaining agreement are not met by noon on Nov. 14, fueling concerns about a potential diesel shortage next month.

The BP refinery in Rotterdam processes around 400,000 bbl of oil annually and is an important supplier of diesel to northern Europe.

"If we don't receive a reaction from BP about our ultimatum and our demands, then we will proceed to action," said spokesman Jaap Bosma of the CNV union in an interview. CNV represents 440 of the 730 workers at the refinery and says it has a mandate from them to strike.

BP said it remains in discussions with the unions and is hopeful of a resolution. "We regret that we have not yet reached an agreement and that actions may follow," the company said in an emailed statement.

"We are convinced that we have offered a fair, market-based proposal...Naturally, we will remain in dialogue to reach an agreement soon."

Bosma said BP's final offer for a new collective labor agreement under discussion since April had been for a 5% wage increase and a one-time bonus of 4,000 euros ($4,000).

With Dutch inflation running around 15%, workers are seeking a 6% increase, the 4,000-euro bonus and also an equity compensation package that would amount to another 3.5% pay increase, Bosma said.

Market observers and the Dutch government have warned of possible diesel shortages after Russian crude is banned from European ports in early December.