Seven former heads of the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy—from both Republican and Democratic administrations—teamed up on Thursday to warn Congress that the Trump administration's budget could do "serious harm" to America's energy future.

"The U.S. Department of Energy is the single largest funder of clean energy innovation in the United States," they wrote. "Our nation will be hindered in the global energy market without a strategic and well-funded DOE research portfolio, including basic science, energy efficiency, renewable energy, nuclear energy, fossil energy and electricity reliability."

EERE, which oversees the National Renewable Energy Laboratory, leads the nation's research and development into clean energy technology and sustainability, while aiming to increase the generation of electricity by renewable sources. It helped drive the expansion of rooftop solar panels, electric vehicle batteries and LED lighting, supports funding for innovative energy technologies, and has set federal appliance and efficiency standards that will save consumers nearly $2 trillion between 1987 and 2030.

In a letter sent to the members of the U.S. House and Senate appropriations committees who oversee the energy subcommittees, the men and women who headed EERE under presidents George H. W. Bush, Bill Clinton, George W. Bush and Barack Obama outlined the work done by the agency and why it is critical to the country's energy independence.

The budget proposal that President Donald Trump released in May called for a 5.6 percent cut to the Energy Department as a whole, but with a disproportionate amount taken from EERE. Trump's budget, which still has to be negotiated in Congress, calls for a 69 percent cut from fiscal year 2017 levels, which would drop the office's funding from $2.069 billion in 2017 to $636 billion in 2018.

"We are unified that cuts of the magnitude in the proposed FY18 budget will do serious harm to this office's critical work and America's energy future," the former EERE leaders wrote in the letter, which was first reported by the Washington Post.

Trump's proposed cuts come at a time when other countries—China in particular—are becoming global leaders on clean energy, often relying on technologies first developed in the United States with EERE's research and development funds.

"It is telling that China intends to spend more than $360 billion on renewables through 2020 and create 13 million jobs," they wrote. "We ignore China's resolve—and success to date—at our peril."

The business community sent a similar message to Congress and the Trump administration this week. A group of 14 senior business leaders in technology, finance and energy—including the head of the U.S. Chamber of Commerce and the chairman of Shell—asked that Congress continue its funding of research and development, particularly in energy.