The NTS oversees everything from buildings to the islands of St Kilda
Critics of the National Trust for Scotland have urged it to drop its "old discredited policies" and set a new course.
The call came as the NTS prepared to hold its AGM against the background of a bitter dispute over its departing chairwoman.
The In Trust For Scotland campaign group is angry about plans to cut more than 60 jobs and close some properties.
The NTS has said it plans to review its future role and structure.
Despite membership reaching an all-time high, NTS chairwoman Shonaig MacPherson announced at the start of September she was to step down from the post.
Members had tabled a motion of no-confidence.
In Trust For Scotland has issued an open letter ahead of Saturday's AGM calling for the upcoming governance review to address the "fundamental need for effective management".
It states: "Perhaps a first act, without waiting for completion of a governance review, might be immediately to put a structure in place to restore the supremacy of the present council's role and for the future council to truly represent the members' interests and views.
"Its principal role is to govern the trust on behalf of and with the assent of the 315,000 members."
The group's Bill Fraser said: "We believe that although the membership continues to go up, there's got to be a complete radical overhaul of the way the financial system is made up, because that is part of the problem - we simply don't know what is going on, there is no openness."
Earlier this month, NTS chief executive Kate Mavor told MSPs on Holyrood's economy committee the trust's finances were sound and it was ready to "move forward with confidence".
She also stressed that the organisation had opened its accounts to anybody who wanted to find out what goes on behind the scenes.
Speaking to BBC Scotland ahead of this weekend's AGM, she added: "There is a very severe recession and that means things have to change and that is what is happening at the National Trust for Scotland.
"We have to make changes and make sure we are fit for purpose for the years ahead."
Culture Minister Mike Russell said it was not for government to interfere in the trust's workings but that he recognised elements of its "complex and Byzantine" governance needed to change.
Mr Russell said: "At the end of the day the trust has to solve its own problems, come together as an organisation, a membership organisation with huge responsibilities but huge opportunities, and move forward.
"What I've also offered is the opportunity to work closely with the state sector in heritage, Historic Scotland is a large player within this area, I don't believe that Historic Scotland and the National Trust are in competition.
"I believe that together, working together, doing some joint work together, we could be even stronger."
The minister said this could include combined access to sites for members of both organisations.
He added that the prospects for the NTS working with Historic Scotland and private owners were great, but that members, staff and management had to come together to achieve this.
The NTS looks after more than 100 historic properties, which showcase Scotland's architectural heritage.
In May it said planned redundancies had been reduced from 91 to 65 full-time jobs after talks with staff and unions.
But the trust said 46 seasonal jobs would be cut, with 16 other posts in doubt, while Hutchesons' Hall in Glasgow, Leith Hall in Aberdeenshire, Ben Lawers visitor centre and Hill of Tarvit Mansion House in Fife would close.
It has also been trying to sell its Category A-listed headquarters in Charlotte Square in Edinburgh.