American Electric Power (AEP), one of the largest electricity utilities in the US, is to ditch its membership of the American Legislative Exchange Council (Alec), a rightwing organisation that has consistently opposed the deployment of renewable energy and action on climate change.

A spokeswoman for AEP told the Guardian that the decision was made as the company attempts to help implement the Clean Power Plan, the Obama administration’s strategy to curb carbon dioxide pollution from the nation’s power plants.

“We let (Alec) know that we won’t be renewing our membership in 2016,” she said. “We are reallocating our resources as we focus on our work with the states around the Clean Power Plan. There are a variety of reasons for the decision. We have long been involved in the reduction of greenhouse gas emissions.”

AEP is the latest business to flee Alec, with Royal Dutch Shell specifically citing the controversial organisation’s stance on climate change as a reason for ending its membership. BP also recently ended its involvement with the free-market lobby group, while companies including Amazon, Coca-Cola, McDonald’s, Facebook and Google all left the organisation over its stance on gun control in the wake of the 2012 killing of teenager Trayvon Martin.

Alec has backed legislation penalising homeowners who install solar panels, labelling them “free riders”, and has lobbied heavily against the Environmental Protection Agency, which is Barack Obama’s primary tool for reducing greenhouse gases, to the point of considering the agency’s complete elimination. Alec also disputes the theory that pesticides are harming bees.

The conservative group has rejected allegations it denies climate science but its official position on the issue states that climate change is “a historical phenomenon and the debate will continue on the significance of natural and anthropogenic contributions.

“Unilateral efforts by the United States or regions within the United States will not significantly decrease carbon emissions globally, and international efforts to decrease emissions have proven politically infeasible and unenforceable,” the position statement added.

Campaign groups have repeatedly called on businesses to distance themselves from Alec at a time when the Republican party and associated conservative thinktanks are increasingly isolated in the global effort to head off the worst effects of climate change. The Union of Concerned Scientists has criticised Alec’s “extreme and non-science-based position on climate change” that it says is at odds with most large businesses.

American Electric Power is the sixth-largest US electric utility by market capitalisation, with the company serving nearly 5.4 million customers in 11 states in the country’s midwest and south. The business, which has around 32,000 megawatts in generation capacity, insists it is on track to reduce its emissions by 25% by 2017, based on 2005 levels.

Nearly three-quarters of AEP’s generation was supplied by coal in 2005 but this is expected to drop to 51% next year, with renewable energy such as wind and solar comprising 11% of generation.

A company spokeswoman said AEP was previously concerned by the EPA’s plan to slash carbon emissions from power plants but only due to the pace of the proposed changes. AEP supports the EPA’s amended plan and the expansion of renewables in general, the spokeswoman added.

Melinda Pierce, legislative director at environment group the Sierra Club, said: “AEP, a major American electric utility, is long past due in finally joining Google, eBay, Facebook, and even oil giants BP and Shell by cutting ties with this highly controversial organisation.

“It’s time for other major companies like UPS, State Farm, and Pfizer to immediately follow suit and demonstrate their own corporate responsibility. Alec is determined to thwart or eliminate essential environmental safeguards that protect clean air, clean water, and our climate.”

The news of AEP’s scrapped membership follows Alec’s states and nation policy summit, which concluded on Friday in Scottsdale, Arizona. The gathering featured a speech from Republican presidential candidate Ben Carson, who told the audience that the US needed to be “aggressive” in its pursuit of Islamic State, that police officers have got “a bad rap” from sections of the media and that there needs to be a flat tax on all income levels.

Carson patted a nearby bust of Thomas Jefferson, who he called a “genius”, during the speech. “We need to buy that debt down, we need to have fiscal policies that make sense, we need a balanced budget amendment,” Carson said.

A spokesman for Alec said: “It has been a great year for Alec with nearly 500 new Alec member legislators and 43 new stakeholder groups joining in the robust exchange of ideas during calendar year 2015.

“Alec member legislators are more professional, more involved and more engaged than the average state legislator, and companies that depart – as a result of strategic shifts or any other reason – will unfortunately be absent from the educational exchange undertaken at Alec meetings.”