Chelsea Clinton is among a handful of Clinton insiders whose emails are being sought in a new Freedom of Information Act lawsuit filed against the State Department.

The case, which was filed in federal court Thursday by Citizens United, asked for all emails sent under the name "Diane Reynolds," an apparent pseudonym Clinton used to protect her identity when communicating with members of the State Department.

Chelsea Clinton worked as vice chair of the Clinton Foundation while her mother served as secretary of state, further blurring the lines between the charity's philanthropic work and Hillary Clinton's diplomatic efforts.

The conservative watchdog group asked the State Department for records of Chelsea Clinton's communications with high-level agency officials, including Cheryl Mills, Huma Abedin and Jake Sullivan, three of Hillary Clinton's closest aides.

The lawsuit also requested emails between Chelsea Clinton and Kris Balderston, a State Department official tasked with, among other things, drumming up private investments for a diplomatic project that put the foundation's donor network at the center of a high-profile State Department event.

Citizens United, which has filed a series of lawsuits over FOIA requests that have gone untouched by the State Department, sued the agency over requests for emails from other top Clinton Foundation employees, such as Amitabh Desai, and aides to Hillary Clinton who were frequently in contact with the charity.

Chelsea Clinton has emerged as a campaign surrogate for her mother as the Democratic primary in Iowa tightens between Hillary Clinton and Sen. Bernie Sanders.

At the same time, the foundation for which Chelsea Clinton works has come under fire amid reports that the FBI expanded its investigation to include allegations of "public corruption" at the charity.

While Hillary Clinton has denied the existence of such a probe, emails made public through FOIA lawsuits so far indicate Clinton Foundation employees did occasionally work their contacts in the State Department to secure meetings and favors for charity donors.