A group of Democratic senators and one Republican, as well as two Democratic House committees, sent letters on Monday to the National Science Foundation asking it to reverse course on its plan to dismantle a sprawling ocean monitoring network, with House lawmakers going further and accusing the agency of acting illegally.

The Ocean Observatories Initiative is a network of more than 900 ocean sensors built at a cost of $386m. Over the last decade it has tracked ocean circulation, marine ecosystems, climate change and extreme weather, producing data freely available to the public and informing more than 500 scientific publications. The project was slated to run another 15 to 20 years.

The National Science Foundation had directed the removal of most of the system’s instruments from waters off Oregon, Washington, Alaska, North Carolina and Greenland by 2027 – a decision scientists said came with no warning and no scientific review. The independent federal agency, which was established by Congress, described the move not as a cancellation but as a “descoping” aligned with a strategy to prioritize “evolving scientific priorities and emerging technologies”. The Trump administration’s proposed 2026 budget had included a 55% cut to the agency.

“It just seems like this is supreme stupidity and a violation of the fundamental distribution of powers in our Constitution,” Jeff Merkley, a Democratic senator of Oregon, told the Associated Press. “This program is authorized, it’s funded, and for the administration to shut it down without direction from Congress violates that vision in which the people’s representatives decide what’s done and funded, and the executive branch executes that vision.”

Merkley and Republican senator, Lisa Murkowski of Alaska, co-led the letter , which was also signed by Democratic Senators Edward Markey and Elizabeth Warren of Massachusetts, Tammy Baldwin of Wisconsin, Patty Murray and Maria Cantwell of Washington, Sheldon Whitehouse of Rhode Island, Chris Van Hollen of Maryland and Ron Wyden of Oregon. It urged the National Science Foundation, or NSF, to halt the dismantling of the Ocean Observatories Initiative and conduct a thorough review, including consultation with the marine science community, before any further action is taken.

“Eliminating most of this complex ocean monitoring system threatens the safety of our coastal communities while undermining our nation’s ability to monitor coastal environments, marine currents, and extreme weather events,” the senators wrote.

In a sharper rebuke, Democrats from the House science, space and technology committee and the House natural resources committee sent a joint letter demanding the agency “cease this expensive, destructive, and – crucially – illegal action at once”. The letter was led by Zoe Lofgren and Jared Huffman, representatives of California, the top Democrats on their respective committees and was signed by 23 Democratic members from each panel.

In a 3 June statement, the NSF said its decision drew in part on a 2025 National Academies report on the future of ocean science. “NSF remains committed to ocean science and will continue working with the scientific community on high-priority research objectives,” it wrote.

The ocean observatory cuts are part of a broader retreat from environmental and climate-related science under Donald Trump’s Republican administration, which has moved to scale back research programs, reduce staffing at agencies including the National Oceanic and Atmospheric Administration and the Environmental Protection Agency, and ease emissions regulations.

Federal appropriations law requires the NSF to notify the House and Senate appropriations committees at least 30 days in advance of any planned decommissioning of agency owned facilities or assets valued at more than $2.5 m. The House letter said no such notification had been transmitted.

Merkley said he learned of the dismantling through news reports.

“It was like the alarm bells just went off,” he said. “None of us knew about this, and there didn’t appear to have been any consultation or any scientific commission or stakeholders that were leading to this.”

Merkley said his office is still confirming whether formal notification was given, but he added: “If there was no notification, this would appear to be illegal.”

He and Murkowski planned to file legislation on Monday that would prohibit the NSF from spending federal funds to decommission instruments until a thorough review has been completed.

Scientists are scheduled to begin pulling the first buoy off the Oregon coast on Tuesday.

In their letter, the senators cited the approaching El Niño – a periodic Pacific warming that disrupts weather patterns and supercharges marine heat waves – as evidence the cuts are particularly ill timed.

“The loss of this deep-water observation system would threaten our ability to prepare for and monitor future El Niño events,” they wrote, warning coastal communities, fishermen and emergency responders would be left without crucial information.

“Instead of paying for the valuable insights that can be gleaned from the 10-years-and-counting continuous monitoring, taxpayers are now paying for research vessels to span the ocean dredging up hundreds of pieces of instrumentation. This is pathetic,” the House letter states. “In a time of strained resources, the NSF is wasting time and money to destroy its own scientific infrastructure.”