Scientists, health experts and environmental groups have condemned new legislation negotiated in secret by the fossil-fuel-friendly Democratic senator Joe Manchin and the Senate leader, Chuck Schumer, which will fast-track major energy projects by gutting clean water and environmental protections.

The permitting bill published on Wednesday was the result of a deal between Manchin and Democratic leaders, which secured the West Virginia senator’s vote for Joe Biden’s historic climate legislation, the Inflation Reduction Act, which Manchin held up for months.

The bill mandates all permits for the Mountain Valley pipeline (MVP), a project long delayed by environmental violations and judicial rulings, be issued within 30 days of passage and strips away virtually any scope for judicial review.

Democratic leaders want to push through Manchin’s bill without debate or analysis, and are expected to attach the legislation to a funding measure Congress must pass before 1 October.

Energy industry associations have widely welcomed the reforms but opposition from Democrats and Republicans could scupper the deal.

Critics say the bill is a giveaway to the fossil fuel lobby, paving the way for oil and gas production that will stop the US meeting its obligations to cut greenhouse gases and lead to further environmental injustices for people of color, Indigenous communities and low-income areas. It slashes judicial and state powers and oversight, handing Washington greater control over major projects.

“This is not permitting reform,” said the Greenpeace USA co-executive director Ebony Twilley Martin. “This is permitting a giveaway that benefits those who continue to line their pockets at the expense of those affected by climate disasters. Our country cannot afford any new oil, gas or coal projects if we’re going to avoid climate catastrophe.”

On Thursday, more than 400 scientists, doctors and nurses delivered a letter imploring Schumer and the House speaker, Nancy Pelosi, to reject the deal. “The scientific consensus is now crystal clear … fossil fuel projects carry enormous risks to public health … we need to leave oil, gas and coal in the ground and turn off the spigot of carbon pouring into the air.”

Jennifer K Falcon, an Indigenous environmentalist from the Ikiya Collective, said: “Our communities have already lost so much from environmental racism but there is so much to save. [They] are not sacrifice zones for corrupt politicians like Manchin and Schumer who benefit from big oil’s windfall profits.

“The science is clear about the worsening climate crisis. We have no time to waste on dirty side deals.”

Manchin has received more campaign contributions from fossil fuel industries than any other lawmaker this election cycle, according to Open Secrets.

The legislative side deal requires Biden to designate at least 25 energy projects of strategic national importance for federal review within 90 days of passage. The projects must include at least five that produce, process, transport or store fossil fuels or biofuels, as well as six that are not fossil fuels and four mining projects.

The bill mandates a two-year limit on environmental reviews for major projects – regardless of their complexity and potential for harming the environment, water supplies and human health.

According to Brett Hartl, government affairs director at the Center for Biological Diversity, the bill contains the most significant loss of protections under the bedrock National Environmental Policy Act (Nepa) and the Clean Water Act since at least the last Bush administration, when Republicans had full control of Congress.

“Any member of Congress who claims this disastrous legislation is vital for ramping up renewables either doesn’t understand or is ignoring the enormous fossil fuel giveaways at stake,” Hartl said.

The bill was negotiated under a cloak of secrecy. Passage through the Senate is far from assured. A small group of progressive Democrats are looking to separate Manchin’s legislation from the stopgap funding bill, so they can vote against the permitting bill without voting to shut down the government.

Senator Jeff Merkley of Oregon has organised a letter to Schumer, with the support of Tammy Duckworth of Illinois, Cory Booker of New Jersey, Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont – a move that mirrors a similar plea by 77 House progressives earlier this month.

The letter, which was leaked to Politico, states: “We have heard extensive concerns from the environmental justice community regarding the proposed permitting reforms and are writing to convey the importance of those concerns, and to let you know that we share them.”

On Tuesday, Schumer said he planned to add permitting reform to the spending bill and “get it done”.

But Republicans who want more radical regulatory and permitting reforms may also vote against the bill, which requires 60 votes to move to the House. Earlier this month, 46 Republicans signed on to an alternative permitting bill introduced by the other West Virginian senator, Shelley Moore Capito.

Schumer’s decision to capitulate to Manchin has angered progressives.

Manchin agreed to back his party’s historic climate legislation before the midterm elections but only after negotiating a side deal to fast-track the MVP, a shale gas pipeline which would stretch 303 miles across the Appalachian mountains from north-western West Virginia to southern Virginia.

Before construction was suspended, the MVP had produced more than 350 water quality violations. Manchin’s bill exempts the MVP from the Endangered Species Act, which experts say will push two species – the Roanoke logperch and the candy darter – much closer toward extinction.

On Wednesday, the Democratic senator Tim Kaine, of Virginia, said he could not support the “highly unusual provisions” regarding the MVP which “eliminate any judicial review”. Kaine said he had been excluded from talks, even though 100 miles of the pipeline would run through his state.

Raúl Grijalva, chair of the House natural resources committee, said: “These dangerous permitting shortcuts have been on industry wishlists for years. And now they’ve added the Mountain Valley pipeline approval as the rotten cherry on top of the pile.

“The very fact that this fossil fuel brainchild is being force-fed into must-pass government funding speaks to its unpopularity. My colleagues and I don’t want this. The communities that are already hit hardest by the fossil fuel industry’s messes certainly don’t want or deserve this. Even Republicans don’t want this. Right now, our focus should be on keeping the government open, not destructive, unrelated riders.”

In favor of the bill Gregory Wetstone, chief executive of the American Council on Renewable Energy, said it “includes provisions that will help streamline the transmission approval process, improving our ability to meet our nation’s decarbonisation goals”.

Heather Zichal, chief executive of the American Clean Power Association, said: “Our current permitting system is overly cumbersome and mired in delays, hamstringing our ability to grow the clean energy economy.”