The Interior Department’s internal watchdog has opened a formal investigation into alleged violations of federal ethics rules by six high-ranking agency officials who maintained close ties to former employers.

Mary Kendall, the agency’s deputy inspector general, confirmed the probe in an April 18 letter to the Campaign Legal Center, the D.C.-based nonpartisan nonprofit that named the officials in a 19-page complaint filed in February.

“After reviewing the information you provided, in addition to other information available to us, a related investigation has been opened,” Kendall wrote.

In its complaint, which cites two HuffPost reports, the center wrote that the high-ranking employees’ alleged violations “suggest a disturbing pattern of misconduct” across the agency.

Delaney Marsco, a legal counsel for ethics at the Campaign Legal Center, said in an email statement Tuesday that the investigation “confirms that political appointees at the agency have been disregarding the ethical obligations of public service.”

“An agency’s ethical culture depends on ethical leadership. Former Secretary Ryan Zinke and Secretary David Bernhardt, now under investigation himself for ethics violations, have failed to demonstrate adequate ethical behavior at the top of Interior,” Matsco said. “We hope this investigation will answer whether these officials are working on behalf of the American people or on behalf of the interests that used to pay their salary.”

Interior did not immediately respond to HuffPost’s request for comment on Tuesday. But spokeswoman Faith Vander Voort told The Washington Post that the agency “takes ethics issues seriously” and its own ethics officials were consulted after the Campaign Legal Center filed the complaint.

“Ethics reviewed each matter, and provided materials to the Chief of Staff, who has taken appropriate actions. All of these materials have been provided to the Inspector General,” Vander Voort told the newspaper. She declined to specify what specific actions were taken.

News of the probe comes as Bernhardt, a former oil and gas lobbyist who was confirmed as secretary of the Interior Department less than two weeks ago, is scheduled to appear at the White House on Tuesday afternoon for a ceremonial swearing-in. This is the second formal inspector general investigation since Bernhardt’s confirmation. The watchdog informed lawmakers in a letter last week that it is looking into Bernhardt’s conduct after receiving seven complaints “alleging various potential conflict of interest and other violations.”

Bernhardt is among several Interior officials who have been accused of violating President Donald Trump’s ethics pledge, which bars political appointees in the executive branch from participating in certain matters involving former employers or clients for two years. He maintains he has complied with all ethics rules and has touted his efforts to improve the agency’s “badly neglected” ethics infrastructure.

The center’s complaint and the new probe are based in part on HuffPost’s reporting on seemingly clear violations of ethics rules by two Interior officials: Lori Mashburn, the agency’s White House liaison, and Ben Cassidy, the department’s senior deputy director for intergovernmental and external affairs.

Mashburn attended two private events hosted by her longtime former employer, the right-wing Heritage Foundation. Those included joining Zinke at an Oct. 16, 2017, foundation affair that it described as “an exclusive briefing for members who support Heritage with gifts of $10,000+ annually or legacy commitments of $200,000+.” Mashburn worked as an associate director at Heritage from October 2011 to January 2017.

Cassidy, a longtime lobbyist for the National Rifle Association, participated in several agency meetings dealing with issues that he had lobbied Interior on while still with the NRA, including trophy hunting and national monument designations. He also served as a point person for members of a hunting advisory council, including one of his former NRA colleagues.

The ethics pledge for Trump appointees also prohibits former lobbyists from participating in any particular matters they lobbied on in the two years before being appointed.

As HuffPost reported in February, the Campaign Legal Center complaint also names:

Doug Domenech, the assistant secretary for insular and international affairs at Interior and a longtime Republican operative who served in George W. Bush’s administration. For nearly two years before joining the agency, Domenech worked as the director for the Fueling Freedom Project at the Texas Public Policy Foundation, a conservative think tank linked to Charles and David Koch. Official agency calendars show that in April, while still an adviser to Zinke, Domenech met twice with representatives of the Texas Public Policy Foundation to discuss issues about which his former employer had ongoing litigation against Interior, as Pacific Standard first reported in May. Six months after those meetings, Interior settled one of those lawsuits in what the foundation called a “major win for private property rights.”

Vincent DeVito, a former energy counselor to Zinke. DeVito participated in an August 2017 meeting with a former client, Boston-based Eversource Energy. He left the agency in August and quickly took a job at an independent offshore oil and gas company.