Foreign Secretary Margaret Beckett has been criticised for not giving evidence to an influential group of MPs about the government's Europe policy.
Margaret Beckett had declined to appear so close to the summit
The foreign affairs committee said her reluctance to attend a session ahead of an EU summit, was "a failure of accountability to Parliament".
Europe Minister Geoff Hoon also came in for criticism from the committee.
A spokeswoman for Mrs Beckett said she took accountability to Parliament very seriously and always kept it informed.
She has said she would appear a few days before the summit which starts on 21 June, but committee chairman Mike Gapes, who said he had been asking for an appearance since February, objected to the timing.
"By then senior officials in the Foreign Office and Number 10 will have been involved in months of discussions with their counterparts in other European countries," he told BBC Radio 4's Today programme.
"There are controversial issues here - in the past there has been a commitment to a referendum, if we are now moving away from a referendum and we are having parliamentary decisions on these processes, then Parliament itself has to be fully engaged in the discussion and the development of the policy."
He wrote to Mrs Beckett on behalf of the committee expressing "deep concern".
The summit will consider attempts by Germany to revive the EU constitution, vetoed by the French and Dutch in referendums two years ago.
In the letter Mr Gapes said: "The committee regards the refusal of the [Foreign Office] to provide a minister to give oral evidence during this crucial phase of the discussions on the future of Europe as a failure of accountability to Parliament."
He said Mr Hoon had suggested two dates to appear before the committee in May, which were not followed up.
"It is the strong view of the committee that an evidence session in June is too late," Mr Gapes wrote.
A spokeswoman for Mrs Beckett said she and her ministerial term took their responsibilities to Parliament and the committee "very seriously".
"Our position was that any evidence session would be most useful once the German presidency had set out their timetable for discussions leading up to the European Council and once the government had drawn up a set of policy options in response," she said.
"Ministers continue to keep Parliament informed both through written questions and through monthly foreign office oral questions."
And a source close to Mr Hoon said he was "bending over backwards" to accommodate the committee, and had offered to appear during the weeks beginning 28 May and 4 June, as well as on either 13 June and 18 June.
"Geoff Hoon has always been very happy and remains happy to appear before the committee to discuss the EU constitutional treaty."
Shadow Europe minister, Mark Francois, for the Conservatives, said he agreed with the committee's criticism.
"The government has not only been secretive, they haven't even set out clear goals for Britain in the talks on a new Treaty.
"Either they don't want to tell the British people what they want to sign up to or they don't have a clue what they actually want."