At their last meeting, members of Falkirk Council voted to bring all leisure, sport and cultural services - including libraries, swimming pools, gyms and museums - back in-house for the first time since the Trust was formed in 2011.
Ian Scott, Trust chairman for the first six years, cannot understand why councillors took such a huge decision without any consultation and knowing the financial costs are "staggering".
In a letter to The Falkirk Herald, the former board members ask councillors to reconsider.
They write: "We strongly believe that this action will inflict huge financial damage on our community and set sports, culture and arts development back for years to come."
The Trust's charitable status means it can claim more than £1 million every year in non-domestic rates relief and Mr Scott believes that losing that amount of money is "irrational".
"They do not seem to have taken any account of the huge costs that are involved," he said.
"The headline figure that will be lost is £1 million but when the Trust was put together ten years ago the legal costs were enormous and it will cost even more now to unpick it.
"If you add in the grants the Trust was able to get because of its charitable status, it's an enormous amount of money - and this is real money that will have to found from somewhere!"
Other signatories to the letter are Bob Tait, who was awarded an MBE for his services to music; Ruth Morrison, who took over from Mr Scott as chair in 2017; and Alex McQuade, former president of Falkirk rugby club.
SNP and Conservative councillors argue that bringing the Trust back in-house will make it more democratic.
But the former board members disagree.
"It will take our community back to the days when councillors decided everything and our vital services become political footballs at the mercy of whatever party can cobble together a majority at any particular moment," they say.
Mr Scott said: "The suggestion that this will bring greater democracy is a complete red herring.
"Every plan put forward by the Trust has to be put forward by the council in advance and any expenditure or changes in service have to be signed off.
"The thing that struck me is that sports, arts and culture were getting a closer examination in greater detail than they had ever had before the Trust was formed."
"The councillors are basically reverting back to the view that they know best about everything and that consultation with the public or direct public involvement is something they don't like."
When the Trust was formed, the idea was that its charitable status would mean it could apply for funding that was not open to the council.
Over the years, however, critics have said the amount of money gained was less than had been promised.
Mr Scott said: "I think it's true to say that we did expect at the beginning there would be more money available to us.
"But that was 2011 and we were coming off the back of the banking crash in 2008 and the situation got very sticky for everybody.
"Nonetheless, the Trust has raised a fantastic amount of money and what you have to remember is that even if you're disappointed with the amount of money raised through grants, if you take it in-house you won't get any money at all."
He added: "When the decision was first made to create they Community Trust, they were taking a gamble - but it was a gamble that would save a million pounds a year.
"Now, the reverse is true - they are taking a conscious decision to lose a million pounds every year."
However, Falkirk Council leader, Cecil Meiklejohn, stands by her view that the change will give elected members more influence over the very difficult decisions that need to be made.
The council is currently conducting a review of its property, in the hope it can close some older buildings to save cash - but the discussions have been fraught and painfully slow.
Mrs Meiklejohn said: "We've had some challenges in getting some decisions over the line and having the views of the Trust is an added complication.
"We have been trying to make better use of our schools and in working with the Trust there have been difficulties on both sides.
"By having a single decision-maker it is hoped it will be easier to make decisions and take away some of the bureaucracy."
In response to the questions raised, Mrs Meiklejohn says a number of efficiencies will mitigate the loss of £1 million, including the cost of having a separate board.
She also believes it is likely that the arrangement for rates relief will change anyway.
Labour group leader Robert Bissett backed the former board members and the Trust itself.
He said: "The Trust increased income from £3 million to almost £8 million a year, allowing us to cut its subsidy, and added £6 million in external funding that wouldn’t be available otherwise.
"The people we serve will be astounded that, facing cuts of £76 million over the next five years, we can afford to throw away this sort of money.
"We will pay for it in jobs and services and make our financial recovery after this pandemic all the harder."