The Scottish Campaign for Freedom of Information in Scotland urged MSPs to back amendments to the proposed legislation that would bring bodies such as housing associations and private companies working on public sector contracts within the scope of Freedom of Information laws.
In a statement, leaders of the group said: "We are hugely disappointed the Scottish Government has failed to use its powers to designate additional bodies for coverage despite undertaking a formal consultation process in 2010 as required by the Freedom of Information Scotland Act".
Scots LibDem leader Willie Rennie, a leading supporter, said: "Access to public information is now an entrenched condition of a modern government's contract with the taxpayer.
"It is only right bodies that spend the public pound face the public's right to scrutiny. That is why Nicola Sturgeon and her MSP colleagues must support moves to broaden the public's access to information."
MSPs are today expected to approve the first changes to the Freedom of Information Act since it came into force in 2005.
A Scottish Government spokesman said: "Scotland already has the most robust Freedom of Information regime in these islands."