Some heavy-duty trucks in California will be forced to take measures to reduce their emissions next year under new measures unveiled by the state regulator.

The California Air Resources Board has announced plans to make engine retrofits mandatory for some vehicles after becoming frustrated with the lack of progress under the existing voluntary scheme.

The move comes as California steps up its efforts to play a leading role in reducing greenhouse gas emissions.

It will also lead to a further deterioration in the relationship between the state legislature and the automotive sector.

Just last week a group of automobile dealers in California's Central Valley and the Alliance of Automobile Manufacturers launched a legal challenge after plans were announced to introduce tough new vehicle emission caps.

These latest proposals to impose retrofits on some diesel trucks are also likely to face opposition.

"Engine manufacturers are going to challenge it," Stephanie Williams, senior vice president with the California Trucking Association, told the Reuters news agency.

Around 60,000 vehicles in California will be affected by the new legislation. The voluntary arrangement saw only 18 per cent fitted with new technology to limit emissions, which is well short of the 35 per cent target.