A conservative watchdog group has called for another federal investigation into Hillary Clinton’s communications during her time as Secretary of State, accusing Clinton of giving special government access to an investor in a deep-sea mining company because of his connections to Clinton’s son-in-law.

The group, called the Foundation for Accountability and Civic Trust (FACT), plans to file a complaint with the U.S. Office of Government Ethics on Monday.

“It appears that then Secretary Hillary Clinton gave a private company special access to the State Department based upon the company’s relationships with Secretary Clinton’s family members and donors to the Clinton Foundation,” the group says in the complaint first obtained by TIME.

The complaint comes two weeks after emails released by the State Department show that Clinton followed up on a special request from Marc Mezvinsky, Chelsea Clinton’s husband.

In May 2012, Harry Siklas, an investor in a deep-sea mining firm called Neptune Minerals, asked Mezvinsky to connect him with officials at the State Department in order to discuss mining regulations affecting his investments. Siklas noted he was lobbying for access on behalf of a friend who had founded the deep-sea mining firm.

“Hey bud,” the Siklas wrote in his note to Mezvinsky. “I need a contact in Hillary’s office: someone my friend Josh (and I perhaps) can reach out via email or phone to discuss mining and the current legal issues and regulations.”

Three months later, State Department emails show, Clinton forwarded the message to another department official. “Could you have someone follow up on this request which was forwarded to me?” Clinton asked in email to Deputy Secretary of State Thomas Nides. “I’ll get on it,” Nides replied.

The email exchange was made public by the State Department’s release of Clinton’s emails and first reported by the Associated Press. Clinton’s email usage is already the subject of federal probes in her and her aides’ handling of classified information on the private server she maintained in her Westchester, N.Y., home.

FACT alleges that the emails appear to show Clinton gave preferential treatment to her son-in-law by following up on the request to give Neptune Minerals an audience with government officials. The emails do not show whether Siklas or anyone at Neptune Minerals succeeded in meeting with Clinton or any other State Department officials. Siklas, the investor who made the request, was also an employee of Goldman Sachs at the time. Goldman Sachs employees were major donors to Clinton’s 2008 presidential campaign.

“We request a full investigation into these communications and a determination of whether any laws were broken,” FACT said in the complaint. Matt Whitaker, the former attorney general of the southern district of Iowa appointed under President George Bush and executive director of FACT said an investigation would help show whether Clinton’s office helped other companies gain similar government access.

FACT is asking the Office of Government Ethics (OGE) to investigate “the circumstances surrounding these apparent unethical communications.” It’s unclear what actions OGE could take. The office does not investigate matters that are within the purview of other inspectors general, and the Department of Justice is responsible for prosecuting criminal offenses. Whitaker said OGE could refer the matter to the Department of Justice.

“We believe that requests like this from anyone other than Goldman Sachs and her son-in-law were not passed along, so there was a preference given in her duty as Secretary of State in comparison to other requests,” Whitaker said.

Whitaker said FACT is nonpartisan and scrutinizes both Republican and Democratic lawmakers. FACT is backed by donors who support conservative legal causes.

The Clinton campaign did not respond to requests for comment.

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