SIPTU has submitted a new planning application to Dublin City Council to replace its headquarters at Liberty Hall with a 22-storey building - which is slimmer but one storey higher than its previous plans for the site.
The union had announced plans to demolish the 17-storey building and rebuild on the site in 2006 as it said the offices were in need of upgrading.
It also pointed out at the time that 40% of Liberty Hall is taken up by lifts, stairways and toilets.
Last year, the union applied to Dublin city council for a new 21-storey building, 24 metres higher than Liberty Hall.
A heritage centre and public sky-deck on the top stories, accessible by a glass fronted sky lift, were part of the planned building.
A conference centre and theatre were also planned with 15 storeys of offices.
However in February, the union withdrew the planning application to allow more time to resolve design issues.
Following consultation, it has submitted a new planning application.
All of key facilities are still in place, however the big difference between the plans is that the main building is slimmer but one storey taller.
Many objections to the first application from organisations such as an Taisce, had centred on the height of the planned building.
Tony Walsh, Head of Infrastructures at SIPTU said the extra floor was only an attempt to get back the floor space they had lost by slimming down the building’s size.
He added that it would fit comfortably into its surroundings.
It is believed that the planning process could take up to a year and, if successful, the redevelopment could take another two and a half years.
SIPTU says it is not disclosing the cost of the project ahead of a tendering process.