Industrial action at the Magners cider factory could disrupt supplies to the UK.
More than 360 staff at brand owner C&C's manufacturing plant in Clonmel, Ireland, are threatening to strike over a 24-hour production schedule.
C&C, which also makes Bulmers in Ireland, says the long hours are needed to meet demand for cider. Staff would work a fortnight on day shift followed by a fortnight on nights, with a 33% premium for the night work.
Unions for the workers have refused to accept the conditions, endorsed by the Irish Labour Court, and will strike unless a compromise is made.