Campaigners fighting for full restoration of the last buildings used by the 1916 Rising leaders have called for detailed assurances on the protection of the entire site.
About 30 people occupied the terrace at 14-17 Moore Street in Dublin from Thursday evening before several hundred people at a street protest heard calls for the Government to explain the redevelopment.
Descendants of the rebel leaders and heritage campaigners fear No 18 will be demolished to make way for a museum entrance next door to a huge shopping complex.
There are also concerns that No 10 and No 13 will not be protected as only 14-17 must be preserved.
Heather Humphreys, Minister for Arts, Heritage and the Gaeltacht, said 13 and 18 and 19 are not part of the National Monument order and are not historically significant.
"The minister is very disappointed that any group would attempt to delay these works and jeopardise the project," a spokeswoman said.
The Save Moore Street campaign described the construction works as a "demolition of history" and vowed to have protesters in the building site until they get adequate commitments on the protection of the terrace.
Among those who took part in the occupation is a grandson of The O'Rahilly, Proinsias O'Rathaille while David Ceannt, grand nephew of Eamonn Ceannt, and Tom Stokes, whose grandfather fought at Boland's Mill, also attended the lunchtime demonstration.
The Government bought part of the terrace last year in a four million euro restoration plan, including No 16 Moore Street where the rebel leaders held their last council of war.
As many as 300 Irish Volunteers and Cumann na mBan members fled into the terrace from the back of the GPO after a bombardment of British artillery set the rebel headquarters ablaze.
Soldiers tunnelled their way through the houses and ultimately surrendered from their base at No 16.
Barry Lyons, honorary secretary of the 1916 Relatives Association, said they felt as though they had been deceived by Government despite assurances that they would be fully consulted and briefed on plans.
"We are fully supporting the occupation, and encouraging it," he said.
"When we were dealing with Minister Humphreys we felt as though we were deceived by what we were told.
"We were told nothing would go ahead without us being informed or without our consultation, but the deal was signed off before our last meeting. While the minister was at a photocall to announce it, we were in Kildare Street being told about it.
"They are going ahead with demolition."
A number of politicians took part in the demonstration including Sinn Fein chiefs Gerry Adams and Mary Lou McDonald, Independent TD Maureen O'Sullivan and People Before Profit TD Richard Boyd Barrett.
The site has been dogged by controversy since being designated a National Monument in 2007 only for planning permission to be granted for a shopping centre on 2.7 hectares from the old Carlton Cinema on O'Connell Street to behind the GPO on Moore Street.
Descendants and campaigners believe the works are being done from plans for the original retail complex next door to what historians regard as a battlefield site.
Proinsias O'Rathaille sent a text to Taoiseach Enda Kenny criticising the decision to allow demolition for the commemorative centre.
"It's an absolute disgrace and a shambles," he said.
Frank Allen, who organised the Arms Around Moore Street campaign, described the works as "turning Anne Frank's home into a Burger King".
The restoration is one project in the Government's plans for the centenary, which also involves 22 million euro being spent on other projects by next Easter to create permanent reminders of the 100-year anniversary.
Ms Humphrey's office said work began on the site in November, but the City Council is responsible for work on the wider Moore Street.
Officials claimed Nos 18 and 19 were in ruins before the Rising and No 13 retains none of its "historic fabric" as the interior has been replaced and the facade is new brick.