It has been dreamed of for decades, planned for years, and in preparation since October 1994: the opening today of the National Museum's new premises at Collins Barracks, Dublin. The restored, 18th-century military headquarters will be a showcase for the Museum's decorative arts, industry and folk-life collections, and illustrate the economic, social, political, and military history of Ireland. The granite barracks complex, overlooking the Liffey at Wolfe Tone Quay has been converted, at the cost of £15 million, into an exhibition centre, which is scheduled to be opened this afternoon by the Taoiseach, Bertie Ahern. "It is a tremendous moment for us - I never thought it would happen," says the Director of the National Museum, Dr Pat Wallace. However, the hundreds of guests invited to celebrate one of the most exciting cultural developments in Dublin for many years will be confronted by the unusual sight of museum curators mounting a picket on the premises, and may be surprised to see some of the displays in an unfinished state. The past week's final preparations for the opening have been clouded by an industrial dispute between the curators of the art and industry collections, which are to be housed at Collins Barracks, and the Department of Arts, Heritage, the Gaeltacht and the Islands. Since last Wednesday the curators, members of the trade union, IMPACT, have been in dispute. They stopped working on finalising the presentation of the exhibits and have held three demonstrations in protest at the failure of the Department to address their grievances. At issue is the overall management structure of the museum, which the curators argue is in need of a radical overhaul - and some form of hierarchy. "At present, there is no middle management in the museum. None of the four curatorial departments has a keeper - what we have is the totally inadequate situation of curators who are in acting, or temporary positions," says Dr Raghnall O Floinn, a curator from the antiquities section, who is the spokesman for the National Museum branch of IMPACT.

"This is not a last-minute action," he says. "We have been trying to resolve it for a year now, but there has been no movement from the Department. The curators are not doing this lightly; they have worked for years on these exhibits. It is a gesture of frustration. We are heartbroken that what should have been a great day for the museum is turning into a funeral." The organisational structure of the museum is unchanged since 1928, in spite of the recommendations of two independent reports by international museum consultants, advocating additional staffing and restructuring. "It's not a question of money," says O Floinn. "The amounts involved are miniscule in the context of the overall budget for Collins Barracks."

A statement issued yesterday afternoon by the office of the Minister for Arts, Heritage, the Gaeltacht and the Islands, Sile de Valera, said she is "keenly aware of the problems and is seriously concerned about the situation.

"The Minister regrets that it has not been possible to resolve this issue. She appreciates the tremendous work done by all the staff, both those involved in the dispute, and others, in bringing the Collins Barracks project to fruition." So, while it remains to be seen whether the Taoiseach will pass the picket today, it is unlikely that many of the distinguished guests from the world of arts and culture will wish to do so.

This is the first phase of the project. Clarke Square, the first section of the museum to be opened, will house decorative art objects including glass and ceramics, as well as extensive silver and furniture collections. Phase Two is scheduled to open in five years' time at a further cost of £14 million, from combined Exchequer and EU sources. Eventually, the entire administration offices of the museum will be based on the site, while the Kildare Street building will continue to house the extensive archaeological collections, including the Stone Age, Bronze Age, Iron Age and Viking artefacts, which will now have room to breathe. The exhibits on display in Clarke Square present the history of Ireland through our material culture, from the 17th century onwards. Most of these artefacts from the national collection will be seen by the public for the first time, having been kept in storage for many years. Many were bequests to the collections held by the Royal Dublin Society and the Royal Irish Academy, before the establishment of the National Museum in the 19th century. Some, such as the exquisite, porcelain Fonthill Vase from 14th-century China, passed through the hands of Hungarian, Italian, French and English nobility, before being acquired by the museum more than a century ago. The uncluttered formality of Col Thomas Burgh's original building has been left intact by the architect, Pat Cooney, from the Office of Public Works, and consultant architects, Gilroy McMahon. Exhibition galleries have been discreetly inserted along two wings of the vast courtyard - formerly a parade ground - which is bordered by a neo-classical arcade. Throughout the three storeys of the museum, modern glass and the original stone are juxtaposed, creating striking contrasts of texture and light, and softening the severity of the building's lines. Inside the galleries, lighting and air is carefully controlled, humidity monitored and dust excluded, to the highest standards of contemporary museum practice. Information boards explain the way the National Museum acquires, conserves, researches and exhibits collections of objects which have associations with a historical person or a place, such as Wolfe Tone's pocket book, Daniel O'Connell's cap, and William of Orange's gauntlets. Now that museums can no longer take their public for granted, increasingly they seek to make their collections as accessible as possible through interactive computer displays and accompanying text, which help to explain the contexts and significance of objects. As the new education officer at Collins Barracks, Helen Beaumont, says: "Museums can be little bubbles. We have a responsibility to reach out to our audience." The aim, as the information boards explain, is "to provide information about attitudes and activities of people in the past" . . . "through the study of our material culture you can learn when, where, why and how something was made, and who used the object. " At Collins Barracks two galleries, named Curators' Choice and Out Of Storage, attempt to explore the question of what a museum is, by revealing the rationale behind curators' selection of objects and demonstrating how the cultural assumptions and priorities of our own era are reflected in the way we collect and display artefacts from the past. It is sad that the scholars and design historians with the specialist knowledge of these collections will not be present today at their triumphant unveiling to the public.