Christmas postal deliveries in the South West could be disrupted if Royal Mail workers vote to strike in a dispute over a new sorting machine.
Almost 1,000 workers at the centre at Filton, Bristol, are to be balloted.
It follows the breakdown in national negotiations over the extension of a trial to operate a new handling system.
Royal Mail said talks to resolve the dispute over the machine which sorts larger parcels, are on-going but union leaders say this is not the case.
David Wiltshire, from the Communication Workers Union (CWU), said a "sensible and mature dialogue" was needed to resolve the dispute.
"A similar machine was installed at Gatwick and members there were given assurances about its use and that's what we want.
"We have never stood in the way of new technology and we have always negotiated staffing levels and safe systems of work," he said.
The new sorting machine was supposed to go live on Monday but its introduction was postponed.
If the ballot supports industrial action, unions would have to give a week's notice of any disruption which could affect last-minute deliveries.
General Manager for Royal Mail in the West of England, Wayne Jay, said he was "disappointed" the CWU had chosen the busiest time of the year to hold the ballot.
"I am optimistic talks being held at a national level on Wednesday will resolve the dispute.
"We have more than 70 people trained to use the new machine and they are eager to use it. The sticking point is in the detail.
"But we do have robust contingency plans in place if needed."