European Union leaders are meeting in Brussels, where they are struggling to reach agreement on new ways to run the 27-member bloc.
Angela Merkel has led calls for a EU members to reach a deal
Germany, which holds the EU presidency, has called for a treaty to replace a planned constitution that was rejected by French and Dutch voters in 2005.
The UK and Poland are both threatening to use their vetoes.
The UK opposes any growth of EU powers, while the Poles are resisting plans to reduce their voting rights.
A draft paper tabled by Germany makes several concessions to EU member states opposed to key parts of the failed constitution.
But both the British Prime Minister Tony Blair - attending his final EU meeting before leaving office next week - and his Polish counterpart have taken a hard line.
Poland's Prime Minister Jaroslaw Kaczynski has suggested that his country deserves a greater share of voting rights than it is being offered under the current draft.
He said Poland was disadvantaged because of the millions of Poles killed by Nazi Germany during World War II.
Under the current system Poland has just two fewer votes than Germany, but under the proposed treaty Warsaw would have a much smaller share because EU votes would be linked to population.
Tony Blair is a veteran of 10 years of European negotiations
Mr Kaczynski argues that his country would be a much larger country now if not for the war, and should therefore qualify for stronger voting rights.
Mr Blair has set out a number of "red lines" which the UK government regards as unacceptable.
These include proposals to make the EU Charter of Fundamental Rights legally binding.
European Commission President Jose Manuel Barroso has warned all member nations to be open to a compromise, and has suggested that the draft treaty would be a "good deal" for the UK.
The German draft paper removes any mention of the word "constitution", accepts that the title of EU-wide foreign minister will not be used, and provides countries with a chance to opt out of EU policies in the area of policing and criminal law.
The Netherlands and the Czech Republic also have concerns about the treaty.
German Chancellor Angela Merkel says every member nation will have their issues addressed at the summit.
But she too urged leaders to move towards a deal.
"Many are watching us, not only in Europe," she said.
"It is important that we don't drag on too long and that we make every effort to reach an agreement."
Correspondents say failure will plunge the EU into a fresh crisis as deep as the one that followed the rejection of the constitution two years ago.
In one early decision, leaders agreed to allow Cyprus and Malta to adopt the European single currency, the euro, beginning in January 2008.