A limited government advocacy group claims in a lawsuit filed Tuesday that the Environmental Protection Agency (EPA) has failed to respond to open records requests for documents related to employee use of encrypted messaging.

Politico first reported in early February that EPA employees were using the encrypted messaging app Signal to determine how to respond to a feared purge of climate science from the then-new Trump administration. Depending on the content of the conversations, those chats may run afoul of record-keeping laws.

The Cause of Action Institute — a group aligned with GOP mega-donors Charles and David Koch — filed several Freedom of Information Act requests for documents relating to the Signal messages, including ones in August and September, for records from software that could detect the Signal app on phones. According to the group, the EPA has not responded either of those requests.

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The institute, which already filed a lawsuit over the documents requested in August, submitted another suit on Tuesday in the Washington, D.C. federal court to compel the release of documents from both requests.

Technically, the EPA has 20 days to respond to a request or say it needs a deadline extension.

According to the group's filings, the EPA asked for a series of extensions to the August request before settling on a final deadline on or around Oct. 27. The institute claims it has never heard from the agency since.

The EPA also asked for a clarification on the other request, issued on Sept. 11, which the institute says it provided on Sept. 20. The institute says it has not heard back from the agency on that request either.

The EPA is not the only executive branch agency accused of flouting records laws by using encrypted chat apps. White House staffers reportedly used the Confide secure messaging app to keep their communications secret until former press secretary Sean Spicer explicitly banned its use.