The conservative advocacy group Citizens United filed a lawsuit on Thursday for access to emails between Chelsea Clinton and her mother, Hillary Clinton, when the latter was secretary of state.

Citizens United filed the lawsuit after a Freedom of Information Act request to the State Department wasn't fulfilled. Citizens United President David Bossie said the group was investigating the links between the Clinton Foundation and the work of the State Department while Hillary Clinton was secretary of state. Chelsea Clinton is the vice chair of the foundation.

The lawsuit covers all emails and other correspondence between Chelsea Clinton and her mother’s top aides at the State Department, including Cheryl Mills, Huma Abedin and Jake Sullivan. The organization seeks emails from other key people in the Clinton circle, according to Politico, including: Clinton Foundation foreign policy chief Amitabh Desai, longtime aide to former President Bill Clinton Justin Cooper, and the manager of the Clintons' New York home, Oscar Flores.

"The real interesting person here is, of course, Chelsea Clinton, who is the lead person. ... We saw that pop up on the grid in all email we received over the past year," Bossie told Politico, referring to other requests and lawsuits by his group. Bossie also noted that there was a connection to Hillary Clinton's 2016 White House bid, saying, "We want to see much more about what Chelsea Clinton was up to because she now has put herself out here on the campaign trail, along with Bill Clinton, as a lead surrogate."

He added: "She is somebody who has been a player, a senior adviser to her mother," he said. "She is an officer, somebody with fiduciary responsibility at the Clinton Family Foundation," according to The Hill.

Emails between Chelsea Clinton and Hillary Clinton have already emerged as part of the investigation into the 2012 terrorist attacks on the U.S. diplomatic compound in Benghazi, Libya. In one email, Hillary Clinton told her daughter the attack was carried out by "an Al Qaeda-like group," a statement Republicans said is at odds with what the secretary of state said publicly, according to Fox News.