The activists are fighting proposals for up to 48 properties next to Lenzie Moss, an ancient area of peatland which has a history dating back to the last ice age.
East Dunbartonshire Council is expected to announce next month whether it will consider allowing planning applications to be submitted for the site.
Lenzie Moss, which was designated a nature reserve in 2009 and is home to several endangered species – such as bog rosemary, rare dragonflies, moths, butterflies, voles, water shrew as well as roe deer, foxes, snipes and skylarks – is one of numerous sites across East Dunbartonshire earmarked for development.
In all, 90% of the sites earmarked for houses in the area are in designated green belt land.
East Dunbartonshire, which includes the affluent suburbs of Bearsden, Milngavie and Bishopbriggs, and several small towns, faces a shortage of public land to meet ambitious affordable homes targets.
With public land in the area being so scarce, the council is being forced to rely on the requirement for private developers to make 25% of properties in their schemes affordable to help meet its target.
It is currently in negotiations with the Scottish Government to in a bid to revise its targets downwards.
As part of the plans, Lenzie Rugby Club would sell its pitch and clubhouse, which border Lenzie Moss, to private developers and then move onto grassland that it owns and which encroaches on to the moss.
The Save Lenzie Moss campaigners insist even this move would upset a fragile ecosystem and jeopardise the main peatland area, which is still recovering from its post-Second World War plundering by the horticultural industry.
With swathes of pitches to the west of Lenzie Moss, there are also concerns the rugby club proposal would create a precedent for future house building on or within the immediate vicinity.
The Save Lenzie Moss campaign said that while it had "every sympathy with the rugby club's desire to raise funds to improve their facilities, the negative effect of this on the community we consider outweighs their objectives".
It also said that while it was lobbying politicians to vote against the proposals, it refused to attack the local authority, claiming it was "caught between a rock and a hard place" due to Government-set targets.
Paul Dudman, chairman of the Friends of Lenzie Moss, said: "Our group is concerned over the possible impact on the moss, which is a raised peat bog of international significance.
"However, it is clear that many diverse groups such as parents of local pupils, walkers, and other residents are opposed to this development for various reasons.
"We hope the councillors who will decide which sites go forward to the next stage of the local development plan take into consideration the level of local opposition."
Derek Cunningham, East Dunbartonshire's development director, said: "The site is only one of more than 60 which have been submitted to the council for consideration.
"No decision has yet been made by East Dunbartonshire Council as to how it will address the shortfall in affordable housing.
"There will, however, be an opportunity for interested parties to express views on the issues, options and sites when our Main Issues Report is published."
No-one from Lenzie Rugby Club was available to comment on the proposals.