Activists from Save Moore Street 2016 said repeated calls for an independent inspection of preservation and construction works on the terrace have been refused by Government officials.
A number of people from the group entered the site and recorded some of the work being carried out on the site where the 1916 Rising leaders held their last Council of War.
The group claimed a banner to commemorate the centenary of the rebellion had damaged external brick work.
However, the Department of Arts, Heritage, and the Gaeltacht said it had reported the campaigners to the gardaí and accused them of breaking the law.
“The people concerned, who have not been identified, vacated the site after the intervention of gardaí,” a spokesman said.
Heritage Minister Heather Humphreys said no reputable conservation professional qualified or able to offer any judgment on the works would have gone on to the site in the manner the protesters did.
The future of the National Monument on Moore St has been at the heart of increasingly bitter legal battles.
A large parcel of land next to it from the old Carlton cinema site fronting O’Connell St to part of the old 1916 battlefield site behind the GPO was given the green light for a commercial development in 2007.
Only numbers 14 to 17 on the terrace were to be preserved under the original order but a High Court ruling in April stalled those plans and the initial construction work on the Government’s proposals for a 1916 Commemorative Centre at No 16. Current work must be restricted to protecting the structure.
A spokesperson for the Save Moore Street campaigners said: “This action took place as part of the continuing and escalating campaign for the creation of a revolutionary quarter in the Moore St area to ensure recognition for those men and women and the values they stood up for in 1916 Easter Rising against the British Empire. No harm on the part of the campaigners came to this declared National Monument.”
Ms Humphrey’s department said the “necessary preservation” works by the High Court were disrupted by activists.
“Works being undertaken to the National Monument are mandated by the High Court and are being undertaken by Lissadell Construction — a specialist contractor of note and award in the conservation of historic buildings,” it said.
“The works are being done under the supervision of the chief archaeologist of the National Monuments Service and her colleagues, who include conservation architects.
“Illegal entry onto the site, such as happened this morning, and the continuous harassment of the employees of Lissadell as they go about this necessary conservation work is, in fact, endangering the monument.”