The growing backlash against the Environmental Protection Agency (EPA) will gather fresh momentum today when a collection of states and conservation groups announce their intent to sue the agency for dragging its heels over greenhouse gas regulation.

Twelve litigants will declare proposed lawsuits over the EPA's failure to decide on whether or not it should regulate carbon emissions from the shipping and aviation industries. The intent to sue is a response to the EPA’s release of an Advanced Notice of Proposed Rulemaking on 11 July, which effectively delayed any decision on regulating greenhouse gases until the next administration.

The announcement accuses the EPA of an "unreasonable and unjustifiable delay ", and promises lawsuits within 180 days if the Agency fails to issue responses to the petitions.

The EPA had been ordered by the Supreme Court to decide whether it should regulate carbon dioxide as a pollutant under the Clean Air Act, following a lawsuit against it led by the state of Massachusetts last year. Environmental law firm Earthjustice then petitioned the EPA last October, asking it to decide that carbon emissions from the shipping industry were damaging to human health. It followed with another petition in December addressing the aviation sector. The deadline for responses ran out in March and June respectively.

California, Connecticut, Oregon, New Jersey, and the Pennsylvania Department of Environmental Protection will sue, along with the California Air Resources Board, South Coast Air Quality Management District, and the City of New York. Earthjustice also represented the Centre for Biological Diversity (CBD), ocean protection group Oceana and Friends of the Earth.

"Congress needs to act, but it is tragic that we have lost the benefit of just reinforcing the laws that we already have," said Kassie Siegel, head of the CBD. "The way is clear for the next administration. They should immediately start regulating. There is no reason in law or logic why we shouldn't reguate this today."

The intent to sue notice specifically does not cover emissions from cars. California, in conjunction with other states and conservation groups, is already suing the EPA for its failure to grant a waiver that would enable states to impose stronger automobile emissions limits than federal standards allow.

"The auto suit set the stage legally based on the findings, which accumulated over years, of the world's leading climate scientists," said a spokesperson for Greenpeace US, which was a litigant in the automobile standards waiver suit, but not in the proposed shipping and aviation suits. "In the past month, we have had confirmation that Johnson as head of EPA has had scientists within the agency remove or redact stronger language on climate science and that Cheney has played a role in this as well."

In further evidence that pressure changes at the EPA is intensifying, four Democratic senators this week requested that the Justice Department investigate EPA director Stephen Johnson for perjury and obstruction of Congress.

"Different NGOs have been nibbling at this [issue] for years in different venues," said the Greenpeace spokesperson, adding that the tide of disapproval against the EPA is now mounting.