Republicans in the US House of Representatives are expanding their request for documents related to a major climate study by the US National Oceanic and Atmospheric Administration (NOAA).

Agency researchers—led by Thomas Karl, director of NOAA’s National Centers for Environmental Information in Asheville, North Carolina—published the analysis last June inScience. After updating and correcting problems with the temperature record, the team found no sign of an apparent pause in global warming that had been described in previous studies.

In October, Congressman Lamar Smith, the Texas Republican who leads the House science committee, issued a subpoena for documents related to the NOAA research. The agency has since provided more than 300 pages of e-mails and other documents produced by political appointees and by NOAA's director of communications, Ciaran Clayton. But NOAA has refused to hand over records of its internal scientific deliberations.

Now Smith is casting his net wider. In a February 22 letter to NOAA, he expressed disappointment with the “slow pace and limited scope” of NOAA's response to his initial request. “The speed with which NOAA has conducted these searches and produced documents creates the perception that the Agency is deliberately attempting to impede and hinder the Committee’s oversight,” he wrote.

Smith is now asking that NOAA provide his committee with documents from other agency officials and offices, including chief scientist Richard Spinrad. In his letter, Smith also demands that the search terms be expanded to include a host of new words, including “temperature”, “climate”, “change”, “Obama” and “Paris”. Smith has asked the agency to deliver all documents by February 29.

Clayton says that NOAA is still reviewing the lawmaker's letter. The e-mails that the agency has released to Smith so far discuss NOAA's communications strategy for the release of Karl's study, which NOAA expected to receive intense scrutiny.

“There is nothing in these materials that would support the notion that substance or timing of the paper was politically motivated,” Clayton said. “Science at NOAA is conducted independently and rigorously, and is protected by a robust scientific integrity policy.”

The Union of Concerned Scientists, an advocacy group in Cambridge, Massachusetts, which obtained the committee’s letter and released it on February 26, called the move “unprecedented and unjustified”.

“It’s perfectly reasonable for the committee to have oversight over any sort of political influence over the science,” says Michael Halpern, programme manager for the UCS Center for Science and Democracy. “What we are looking for is to stop the kind of ham-handed and broad subpoenas that compromise the ability of scientists to communicate frankly with each other.”

As it happens, a prominent group of researchers published a commentary this week in Nature Climate Change that challenges the analysis by Karl and his colleagues. The commentary argues that the rate of warming really has slowed in recent decades.

This article is reproduced with permission and was first published on February 26, 2016.