France, Italy and Germany have written to the European Union's executive asking for a delay or softening to planned curbs on carbon dioxide emissions from new vans, EU diplomats say.

The European Commission is mulling proposals this month that would force van makers such as Fiat and Mercedes to cut emissions from new vans by 14 percent to 175 grams per kilometer by July 2013 or face fines.

But the powerful auto makers have pushed hard for the goal to be gradually phased in and for fines to be weakened, just as they argued last year over curbs to CO2 from cars.

Such investment in energy efficiency is not possible in times of economic crisis, they argue.

Paris, Rome and Berlin asked in their letter last week that the Commission yield to the industry's demands by phasing in the curbs around 2017. The 175 g target has not been challenged.

The governments have deemed it inappropriate to put forward this proposal on light commercial vehicles and have asked to delay it to a more appropriate time, said one EU diplomat. The impact assessment must be more detailed.

The launch of the proposal has been delayed twice in recent weeks as officials in the Commission's industry and environment units wrangle over the details.

An earlier draft of the rules envisioned fines for van makers that overshoot the targets of 120 euros per gram of CO2 per vehicle, but the fines have been cut to around 95 euros in recent talks, EU sources say.

Those that miss by less than 3 grams will receive softer penalties.

The Commission has to decide now between putting forward a diluted version before the end of October, or putting it on hold until next year, a second EU diplomat said.

The three automaking nations are also challenging Commission proposals for a long-term target of 135 g by 2020.

We don't support the long-term target as it is now, said a third source in the negotiations. It must be realistic, cost-effective and based on a thorough impact assessment.

(Additional reporting by Ilona Wissenbach; Editing by Dale Hudson)