Toyota's green halo received a battering yesterday after a coalition of environmental groups launched a campaign to highlight the apparent disconnect between the company's development of greener automotive technology and its opposition to proposed US fuel economy standards.

The coalition, called The Truth About Toyota and backed by nine environmental groups including Friends of the Earth and the Union of Concerned Scientists, has taken out ads in the US criticising the company, launched a website and petition attacking its lobbying activities and written an open letter to the firm's North America chairman and chief executive, Shigeru Hayakawa, urging him to halt attempts to "weaken, delay, or eliminate" the US Senate's proposed standards.

Toyota has built a reputation as a pioneer in the development of more fuel efficient cars, most notably through the success of its iconic hybrid Prius, but it has recently attracted the ire of environmentalists for joining with GM, Ford and Chrysler to oppose legislation that require the US vehicle fleet to average 35 miles per gallon by 2020.

The car manufacturers have claimed the legislation is unrealistic and would effectively limit production of sports utility vehicles and vans – a market Toyota is currently targeting. They are instead backing a weaker set of standards proposed by the House of Representatives that would set a goal of 32 to 35 miles per gallon by 2022.

Josephine Cooper, group vice president Toyota Motor North America, said the 35mpg standards would set "a realistic and achievable deadline" and insisted Toyota had a long history of supporting fuel economy standards.

"We have been an industry leader in fuel efficiency, consistently surpassing federal government standards," she added.

However, The Truth About Toyota campaign insists the company's stance undermines its green credentials and accuses it of applying a double standard whereby it is able to comply with strict Japanese fuel economy standards while opposing "more modest improvements" in the US.

It also argued that the proposed 35mpg standard could be attained using current technologies and that when imposed it would reduce greenhouse gas emissions by more than 200 million metric tons per year in 2020.

Frances Beinecke, president of the Natural Resources Defense Council, one of the groups in the coalition, warned Toyota was jeopardising its green credentials.

"Being seen as a green automaker has been great for Toyota's sales, " he said. "If Toyota expects to keep that image, they should stop lobbying against the strongest fuel economy improvement in over 30 years."

The campaign further highlights the growing risk companies face when adopting strategies of processes that appear to contradict their green marketing campaigns. Nick Rappolt, head of European cleantech at global communications agency Bite, said that Toyota's predicament emphasised the importance of developing a consistent green communications strategy.

"If green marketing is to have value it has to be seen to be representative of the ethos of the company and environmental concerns have to cut across everything the company does," he observed. "It is unchartered territory for firms so we will see plenty of mistakes, but they also have to realise that they must adopt a consistent approach."