As EU environment ministers met Tuesday to discuss the European Commission's "2050 Road map" toward a greener economy, all member states except Poland agreed on the need to do more.
The road map, announced in March, calls for a 40 percent cut in carbon emissions by 2030, a 60 percent cut by 2040 and a 80 percent cut by 2050, compared to 1990 levels.
Delegates in Luxembourg were told a 25 percent cut by 2020 would be the most "cost-effective" way of achieving these longer-term targets, compared to the EU's current pledge of 20 percent.
That proved too ambitious for Poland, where 90 percent of electricity is generated from coal.
"The one that actively said it could not support this language was Poland," an EU source told EUobserver.
"It is unclear where we go from here," the source said, pointing to the unanimity needed for EU decisions in this area and the fact Warsaw is about to take over the EU's six-month rotating presidency.
"The council's work program for the next six months will be established by Poland. Today's result was unexpected."
European environmentalists expressed disappointment at Poland's position.
Poland's move showed a "shocking disregard for climate protection and economic revitalization," John Anderson of the World Wildlife Fund said.