Defense Secretary Ash Carter admitted last week that he used a private email account to conduct official business, and now a government accountability nonprofit wants to see the emails.

Cause for Action, an organization focused on regulatory and fiscal transparency, has filed a Freedom of Information Act-request for all of Carter's correspondence from the account, in addition to other messages.

The D.C.-based nonprofit claims that by using a private account, Carter may have violated provisions of the Federal Records Act, which governs the preservation of official government documents.

Amendments made to the FRA in 2014 forbid government workers to use private email addresses for official business unless the emails are copied to an authorized federal email account.

"When high-ranking government employees use personal email to conduct official business, they keep taxpayers in the dark by shielding their records from requests under the Freedom of Information Act, said Cause of Action Institute Executive Director Daniel Epstein, in a statement.

"As an organization devoted to holding the government accountable—regardless of who is in charge—we are focused on ensuring that Sec. Carter's emails are properly stored and archived for the benefit of the American public."

Carter admitted on Dec. 17 to using a private email on his iPhone for some official business, including "administrative messages," but DoD officials said at the time that the Defense Secretary copied the emails to his government-issued email account.

Cause of Action is seeking the emails sent and received from the private account, text messages and instant messages, communications between Carter and the White House and records showing that the DoD complied with FRA regulations.

ABC recently received 34 pages of Carter emails through FOIA and posted them on its website. The use of private emails for government business has become controversial since it was revealed that former Secretary of State Hilary Clinton used one, as well as a private server, during her tenure.

Pentagon officials were unavailable for comment at the time of publication.