PORTLAND, Ore. (AP) — Oregon's Multnomah County, home to Portland, has added the state's largest natural gas utility to its $51.5 billion climate lawsuit against fossil fuel companies over their role in the region's deadly 2021 heat- dome event.

The lawsuit, filed last year, accuses the companies’ carbon emissions of being a cause of the heat-dome event, which shattered temperature records across the Pacific Northwest. About 800 people died in Oregon, Washington state and British Columbia in the heat wave, which hit in late June and early July 2021.

An amended complaint was filed this week, adding NW Natural to a lawsuit that already named oil giants such as ExxonMobil, Chevron and Shell as defendants. It accuses NW Natural, which provides gas to about 2 million people across the Pacific Northwest, of being responsible for “a substantial portion” of greenhouse gas emissions in Oregon and deceiving the public about the harm of such emissions.

NW Natural said it can't comment in detail until it has completed reviewing the claims.

"However, NW Natural believes that these new claims are an attempt to divert attention from legal and factual laws in the case. NW Natural will vigorously contest the County’s claims should they come to court," it said in an emailed statement.

According to the Center for Climate Integrity, it is the first time a gas utility has been named in a lawsuit accusing fossil fuel companies of climate deception. There are currently over two dozen such lawsuits that have been filed by state, local and tribal governments across the U.S., according to the group.

The amended complaint also added the Oregon Institute of Science and Medicine, which describes itself as a research group on its website, to the lawsuit. The group has opposed the concept of human-caused global warming. A request for comment sent Friday to the email address on its website was returned to sender.

Multnomah County is seeking $51.5 billion in damages, largely for what it estimates to be the cost of responding to the effects of extreme heat, wildfire and drought.

“We’re already paying dearly in Multnomah County for our climate crisis — with our tax dollars, with our health and with our lives," county chair Jessica Vega Pederson said in a statement. “Going forward we have to strengthen our safety net just to keep people safe.”

After the initial complaint was filed last year, ExxonMobil said the lawsuit didn't address climate change, while a Chevron lawyer said the claims were baseless.

When contacted for comment Friday, Shell said it was working to reduce its emissions.

“Addressing climate change requires a collaborative, society-wide approach,” it said in an emailed statement. “We do not believe the courtroom is the right venue to address climate change, but that smart policy from government and action from all sectors is the appropriate way to reach solutions and drive progress.”

The case is pending in Multnomah County Circuit Court.