French President Nicolas Sarkozy is calling on the European Union to tax or limit imports from countries that refuse to cap their greenhouse gas emissions.

In a letter released Tuesday to European Commission President Jose Manuel Barroso, the French leader warned that new EU limits on carbon dioxide emissions could lead European companies to relocate to other countries where limitations are not respected.

"Global emissions would not go down and ... jobs would disappear from Europe," Sarkozy wrote. "The measure would then be neither efficient, nor fair nor economically sustainable."

He said it was "indispensable" that goods coming from countries that refuse to cap their emissions be penalized, either through import taxes or by placing quotas on imports from such countries. Three of the world's biggest economies — the United States, China and India — have not yet subscribed to binding emissions reductions.

"This measure is in any case necessary in order to encourage these countries to join" in the fight against global warming, he said.

The European Trade Union Confederation also called Tuesday for a carbon tax, which it said would be the only fair way to keep jobs in Europe and prevent heavy industry — steel, chemicals and concrete — from moving to regions with lower costs for carbon polluters such as Ukraine, Russia or Turkey.

The organization acknowledged it was unclear whether such a tax would be compatible with World Trade Organization rules — leaving the EU open to possible legal challenges from trade partners.

EU leaders pledged last March to cut carbon dioxide emissions — blamed for global warming — by a fifth by 2020 and replace 10 percent of transport fuel with biofuels. Next week, the European Commission is to set out a package detailing how Europe will reach those targets.

It will set caps for each nation — with western Europe expected to make deeper cuts than the 12 eastern European nations that joined over the last three years.

Greenhouse gas emissions in France, which is heavily reliant on nuclear energy, run 25 percent less per inhabitant than the European average.

Sarkozy, a pro-business conservative, has chided the United States for refusing to sign the Kyoto pact, which requires industrial nations to reduce the heat-trapping gases emitted by power plants and other industrial, agricultural and transportation sources. The agreement targets reductions averaging 5 percent below 1990 levels by 2012.

The French leader has also called on fast-growing developing nations like China and India to do more to reduce their greenhouse gas emissions. Leaders of both nations have insisted reducing emissions is primarily the responsibility of the developed world.