Fears of a possible Guinness shortage have been raised after workers in Dublin threatened to strike over redundancy terms.

Staff at Guinness's St James's Gate brewery are to ballot this week on industrial action in a dispute with the company over the reduction of these terms.

The vote by the 800-strong Guinness Staff Union, the largest in the company, could result in an all-out strike at the brewery and threaten supplies not just in Ireland but also the UK and further afield.

A union spokesman said members were angry over the revision of redundancy terms and the company's refusal to enter negotiations on the changes.

The dispute comes at a time when the company is considering a major reorganisation of facilities, including a possible relocation from St James's Gate to a greenfield site near the city. There is also speculation that the relocation could result in the closure of breweries in Dundalk, Kilkenny and Waterford. Moving operations to one site could jeopardise as many as 300 jobs.

A Diageo spokesman confirmed severance terms had been revised, but added: "Diageo has a long tradition of very favourable terms and conditions for all its employees. The revised terms have been benchmarked across leading businesses in Ireland and have been shown to be fair and equitable."

GSU members rejected the revised terms by a 98% margin, with a spokesman claiming the changes would hit older workers particularly hard. The ballot is expected to take about three weeks, while Diageo is due to outline its business plans at the end of next month.

The dispute comes at a time when Guinness sales are up 6% in Ireland after a slump, and sales worldwide are up 15%. The UK would be affected by any industrial action because of the closure of Guinness's Park Royal Brewery in London in 2005. Since then all Guinness sold in the UK has been brewed in Dublin.