Anti-monarchy campaigners have told Sky News they are launching a crowdfunding campaign in an attempt to get greater access to the Royal Archives.
Republic will use the money to lobby MPs and investigate whether there are any loopholes that could provide the legal basis to open up what they describe as Britain's most secretive institution.
The Royal Archives are kept in the Round Tower at Windsor Castle and include personal and official documents of kings and queens from the past 250 years.
But the archives are exempt from freedom of information requests and only bona fide researchers and academics can apply for further access.
Republic CEO Graham Smith said: "These are documents relating to the history and the job of our head of state, there's going to be all sorts of minutes and documentation and reports and discussions between civil servants, world leaders, those sort of things, that are completely hidden away.
"The British people have a right to know their past, they have a right to properly judge this institution and the people that serve in it and you can only really do that with full access to all the official records."
Documents including King George III's private papers and Queen Victoria's journals have been made public.
But Republic believes all of the records should be transferred to the National Archives at Kew, where papers are released after 30 years and archivists decide what is private or personal.
Author Ben Macintyre, who has written has books about spies and the SAS, thinks the Royal Family take secrecy to a new level.
He said: "This is one of the ironies, the fact that MI5 is considerably more accessible historically than the Royal Family.
"Every year MI5 releases archives that do not have a security implication, do not embarrass living individuals, that do not invade privacy.
"It seems to me that those are the principles that you could very easily apply to the royal archive and say everything else needs to be released."
However, royal author Hugo Vickers believes privacy is a tradition worth protecting.
He told Sky News: "It's much better that these papers should be kept for eventual use, and if they were subjected to rules whereby things had to be opened, quite frankly they wouldn't be put into the royal archives and they'd probably disappear.
"Nobody in public life likes to write even an email these days because it can be subject to the Freedom of Information Act."
Republic will launch the crowdfunding campaign at its annual general meeting in London this weekend.