Over 100 people gathered at the gates of Castletown House in Co Kildare on Wednesday night to stop a van from driving up its avenue.
Campaigners gathered after security attempted to drive up the pedestrian-only route.
Gardaí have said they are aware of a "demonstration involving a small group of individuals".
Locals are opposing plans by developers for a rear car park to be moved to the front of the popular landmark in Celbridge, which they say will affect access to the house and traffic in the town.
The Office of Public Works (OPW), which took over the estate in the 1990s, tried to buy the private lands but were outbid.
There was an agreement with the previous owner, on a five-year rolling basis, which gave access to the car park.
The OPW attempted to agree a lease with the new owner, but there were conditions attached to any new lease which would only run up to next May.
The protest began back in early September when a woman arrived as work started to close the M4 entrance.
Word quickly got out around the town.
Two weeks later negotiations with the new developer failed again.
The local community has since been keeping a presence at both gates, to keep them open for all users.
The Save Castletown campaign claim the OPW "failed" to buy the rest of the lands when it was offered it in 2021.
"Back then they did a strong business case to support the purchase which laid out in clear terms that only the current M4 entrance was suitable for vehicle access," they said in a statement.
"This year the land was sold from one developer to another.
"The new developer will not agree same terms as previous developer with OPW for access to the perfectly good current car park and entrance," they added.
Four TDs representing Kildare-North met with the Minister of State for the OPW Patrick O'Donovan, as well as OPW management, earlier this week to voice their concerns and the concerns of residents.
Campaigners said the meeting offered "no positive suggestions."