A Government panel to review the Freedom of Information Act has been seen as "a major attack on the public's right to know".
This was the warning from the Campaign for Freedom of Information following news the panel is being created.
The group is particularly concerned by the panel's remit to reduce the "burden" of FoI and bring in new measures to protect the confidentiality of government discussions.
A cross-party commission is chaired by the former Treasury mandarin, Lord Burns, and will look at whether there should be a "safe space" within the legislation to protect the advice given to ministers by civil servants.
The five-strong panel – which also includes former Conservative Party leader Lord Howard and Labour ex-home secretary Jack Straw – will publish its findings by the end of November.
The move comes after Justice Secretary Michael Gove told MPs last month that there was a need to "revisit" the act to ensure officials were able to speak candidly to ministers.
Cabinet Office Minister Lord Bridges of Headley said the commission would consider whether there was an "appropriate public interest balance" between the requirement for transparency and need for "robust protection" for sensitive information.
In particular, it would look at whether the operation of the act "adequately recognises the need for a 'safe space' for policy development and implementation and frank advice".
Lord Bridges said that the commission would be able to look at whether change was needed to "moderate" the demands placed on public authorities by the act.
"We fully support the Freedom of Information Act but after more than a decade in operation it is time that the process is reviewed, to make sure it's working effectively," he said in a written ministerial statement.
Responsibility in government for FoI is now being transferred from the Ministry of Justice to the Cabinet Office.
The other members of the commission are Ofcom chairman Dame Patricia Hodgson and the former reviewer of counter-terrorism legislation, Lord Carlile.
Director of the Campaign for Freedom of Information Maurice Frankel said: “The government is clearly proposing to crackdown on FoI. Ministers want certainty that policy discussions will not only take place in secret but be kept secret afterwards.
"They don’t like the fact that the Act requires the case for confidentiality to be weighed against the public interest in disclosure. The Commissioner and Tribunal give substantial weight to the need to protect ongoing government discussions and the frankness of future exchanges.
"But after a decision has been announced they sometimes order disclosure where exchanges are anodyne, the material is old or the case for openness is overwhelming. If that balancing test is removed mistakes, bad decisions and policy failures caused by deliberately ignoring the evidence will be concealed for 20 years.”
The Campaign noted that the FoI Act had been "fully examined" three years ago, by the Justice Select Committee in its post legislative scrutiny of the Act.
It said that the committee reported in 2012 that FoI had proved “a significant enhancement of our democracy”, that the Act was “was working well”, concluded that: “We do not believe that there has been any general harmful effect at all on the ability to conduct business in the public service, and in our view the additional burdens are outweighed by the benefits.”