Last-ditch talks aimed at averting the first strike at the Bank of England in more than 50 years have started at the conciliation service.
Members of Unite working in departments including maintenance and security are set to walk out for three days from Tuesday in a dispute over pay.
The union is protesting at the imposition of a below-inflation pay offer.
A protest will be held outside the Bank's headquarters in the City of London on Tuesday if there is no agreement at the talks being chaired by Acas.
A Bank spokesman said: "The Bank has been informed of industrial action being called by Unite. The union balloted approximately 2% of the workforce.
"Should the strike go ahead, the Bank has plans in place so that all sites can continue to operate effectively. We will continue to have discussions with Unite and hope that there will be a positive outcome."