Kilkenny Castle, one of Ireland's most popular tourist attractions, could be closed by industrial action next week.
SIPTU has served notice on Duchas, the State agency responsible for running the 12th century castle, that it will begin industrial action next Tuesday.
The dispute is about a number of issues including staffing arrangements, pay and increased responsibilities on staff since the opening of the Parade Tower at the castle.
Discussions are due to be held today between SIPTU and Duchas in an effort to avert the action. A spokesman for SIPTU said unless their grievances were dealt with the action could spread to other Duchas sites such as Cahir Castle and the Rock of Cashel.