European Commission President Jose Manuel Barroso says there will be no compromise on plans for EU countries to cut carbon emissions.
He was speaking to the European Parliament after a number of countries complained about targets due to be made public by the commission next week.
French President Nicolas Sarkozy has warned Brussels against "penalising unnecessarily" the prospects of growth.
Mr Barroso said the EU should "put our money where our mouth is".
"Do not expect us to compromise on European interests," he said.
"Both our international credibility and credibility before European Union citizens depend on fulfilment of the targets."
Renewable energy
The new targets are aimed at cutting levels of carbon dioxide by 20% and raising the proportion of renewable energy to 20% by 2020.
Other countries are also understood to have objected to the proposals and business groups fear there could be a knock-on effect for European companies.
Lobby group BusinessEurope says companies will lose competitiveness if they are forced to buy an increasing number of permits to emit carbon dioxide.
The European Trade Union Confederation says up to 50,000 steelworkers' jobs could go if their industry moves to areas with lower costs for polluters.
However, Mr Barroso made it clear that the commission was well aware of the situation.
"It is essential to meet the three central challenges that the European Union faces in energy: competitiveness, sustainability and security of supply".
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