President Klaus has compared EU institutions to the old Soviet bloc
The Eurosceptic Czech President, Vaclav Klaus, says he wants his country to have an exemption from a key EU charter before he will sign the Lisbon Treaty.
Mr Klaus demanded an opt-out from the Charter of Fundamental Rights, similar to opt-outs agreed previously for the UK and Poland.
The demand threatens a further delay over the treaty, correspondents say.
Poland's president is expected to sign the treaty on Saturday. That would leave only Mr Klaus still to sign.
Mr Klaus raised fears about possible property claims by Germans expelled from the then Czechoslovakia after World War II.
EU diplomatic pressure
On Thursday Mr Klaus had called for a Czech "footnote" to be added to the treaty, without specifying what it was. He held talks in Prague on Friday with the president of the European Parliament, Jerzy Buzek.
Gavin Hewitt, BBC News, Brussels
There is an element of farce creeping into the drama of the Czech Republic and the Lisbon Treaty. We now know what President Klaus's conditions are for signing the treaty - or rather I think we do.
To start with, he did not intend to reveal his hand today. He feels he was pushed into it. The Czech president is clearly irritated that, in his view, the Swedish prime minister disclosed a confidential conversation they had yesterday...
After the meeting, Mr Buzek said "probably it is the same position, the same arrangement as it is now for Poland and Great Britain" - countries which negotiated opt-outs from the EU charter.
The Lisbon Treaty is aimed at streamlining EU institutions, to improve decision-making in the enlarged 27-nation bloc.
The treaty incorporates the Charter of Fundamental Rights, which covers a wide range of EU citizens' rights and will become legally binding once Lisbon enters into force. That cannot happen unless all 27 member states ratify the treaty.
"Before ratification, the Czech Republic must, additionally at least, negotiate a similar exemption," said Mr Klaus on Friday, quoted by Reuters news agency.
"I believe that this exemption can be resolved quickly."
He said the charter would "allow (claimants) to circumvent Czech courts and place, for example, property claims by people expelled after World War Two directly at the European Court of Justice," he said.
Mr Klaus has said previously he will not sign the treaty until the Czech Constitutional Court rules on a new legal complaint against it, lodged by senators allied to him.
Creates new post of EU president (President of European Council)
New post of High Representative for Foreign Affairs
More decisions by majority vote, rather than unanimity
Ratified by all member states except Czech Republic and Poland
Only Ireland held referendum on it - twice ('Yes' vote second time)
Took a decade of negotiations
Was intended to take effect in January 2009
The Czech parliament has already approved the treaty.
Swedish PM Fredrik Reinfeldt, current holder of the EU presidency, said on Thursday that Mr Klaus was delivering "the wrong message at the wrong time for the EU".
France has voiced opposition to Mr Klaus's demand.
Poland and the UK negotiated opt-outs to ensure that the charter would not override their courts in certain areas of law.
The BBC's Rob Cameron in Prague says Mr Klaus's announcement is likely to cause deep unease both in the Czech Republic and elsewhere in Europe.
It is the government, not the president, who negotiates international treaties and the Czechs did not ask for an opt-out when the Lisbon Treaty was drawn up, our correspondent says.
Some Czech politicians believe Mr Klaus has now stepped well beyond his constitutional remit. One party leader said on Friday proceedings to impeach the president should start immediately.