The decision to prevent disclosure of Attorney General Lord Goldsmith's legal advice on the Iraq war is being studied by the Information Commissioner.
The government refuses to publish the full legal advice on the Iraq war
Richard Thomas received complaints when details were withheld despite requests under the Freedom of Information Act.
The independent watchdog is expected to study the sensitive advice and decide if secrecy is in the public interest.
A Foreign Office lawyer's resignation letter suggests the attorney deemed the war illegal until the eve of conflict.
The revelations came in a censored part of Elizabeth Wilmshurst's letter, obtained by Channel 4 News under the Act.
It suggests Lord Goldsmith QC originally believed a new UN resolution was needed to make the war legal.
But he reportedly wrote an equivocal letter to Tony Blair on 7 March 2003 saying the war might be illegal and it was safer to get a new resolution.
On 17 March he said the invasion was legal under previous UN resolution, with no new agreement needed.
Ms Wilmshurst quit two days before the war because she believed the invasion was a "crime of aggression".
The ensuing row led to Jack Straw defending Lord Goldsmith's advice in the Commons on Thursday, when the foreign secretary denied the letter showed the attorney general had changed his mind just before hostilities began.
Before 7 March: Lord Goldsmith believed war not legal without new UN resolution, claims Elizabeth Wilmshurst
7 March: Lord Goldsmith tells Tony Blair it would be safer to have second resolution
17 March: Parliamentary answer from Lord Goldsmith says war legal without new resolution
18 March: Tony Blair makes case for war ahead of MPs voting for military action
20 March: Invasion of Iraq begins
Mr Thomas, who oversees the act's operation, said he had received a number of complaints from individuals and newspapers after ministers refused applications under the new act to publish the legal advice.
"We will be going through a process of examining those complaints," he said.
Mr Thomas added that so far he had received about eight complaints about the government's decision, but he would not be drawn on the timing of his investigations.
He added: "We have recently signed a memorandum of understanding with Lord Falconer on behalf of all government departments.
"It sets out the basis for co-operation in the interests of efficiency between my office and government departments.
"The departments will provide my office with all relevant information, including everything that has been withheld or redacted and we undertake to keep it appropriately secure and not to release it to third parties."
HOW TO ACCESS INFORMATION
Put the request in writing
Reply should be offered within 20 working days
Explanation should be offered for any refusals
Information may be withheld for reasons including privacy or national security
Refer to information commissioner if explanation is unsatisfactory
Organisation can be compelled to release the information
Appeals can be made to information tribunal
Ministers announced on 25 January that the full text of the attorney general's advice would not be made public under the act.
Government departments received about 40 requests for the document but ministers said it was protected by legal professional privilege.
The Lord Chancellor, Lord Falconer of Thoroton QC, said in January: "It must be right to maintain confidentiality between lawyer and client - whether it is a solicitor and someone buying a house, a barrister and someone appearing in court or, as in this case, the Attorney General and the government."