Southwark Cathedral has locked people out of a garden that has been cared for by people in the south London community for more than 40 years.
Residents arrived at All Hallows Church and Community Garden in Borough on Monday morning to find the garden gates padlocked.
Members of The Save All Hallows' Campaign said they "could not believe" people had been locked out.
The cathedral said the gates would be locked "on occasion".
Destroyed in war
The cathedral, which owns the church, put up a sign that read: "These grounds are the property of the Southwark Cathedral chapter.
"Access is at the chapter's discretion. These gates will be locked from time to time."
The garden is located on the footprint of the original All Hallows Church that was destroyed in World War II.
A smaller church built on the site after the war is no longer in use.
The church and garden, in Copperfield Street, are facing redevelopment proposals by Southwark Cathedral.
The cathedral is preparing to submit its third planning application in five years to Southwark Council to develop the site.
Petitions mounted on the garden gates in July urging people to save All Hallows attracted more than 300 signatures, campaigners said.
"We cannot believe Colin Slee, the Dean of Southwark Cathedral, has locked our community out of the garden which we have cared for and maintained for 40 years," a spokeswoman for The Save All Hallows' Campaign said.
A Southwark Cathedral spokesperson said: "The chapter has told the residents' campaign group repeatedly over an extended period of weeks that, on occasions, the gates will be locked.
"The chapter has worked hard to accommodate residents' comments but has a duty to make the best possible use of this property as a resource for the work of the cathedral."
Its plans include building a worship space and housing for the cathedral's canon pastor.
The exact details of the plans will be made public when Southwark Council registers its application.