The nonprofit Citizens for Responsibility and Ethics in Washington (CREW) sued the federal government Monday, demanding that it produce documents related to former White House Chief of Staff John Kelly and Caliburn International, the operator of the nation's largest shelter for unaccompanied migrant children.

CBS News reported in May that Kelly had joined the board of directors of Caliburn after leaving the White House. Kelly previously worked for DC Capital Partners, an investment firm that — while Kelly was in the White House and involved in major immigration policy decisions — purchased a company that operated one unaccompanied migrant children shelter in Homestead, Florida. It then folded that company into Caliburn.

In the final six months of 2018, new federal policies helped swell the population of unaccompanied migrant children in government custody as Caliburn rapidly expanded its government-funded program to house them. The operation in Homestead tripled its capacity, becoming by far the nation's largest.

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The CBS News report detailing Kelly's role prompted several further investigations. Senator Elizabeth Warren, D-Massachusetts, who is also running for president, launched an investigation along with Rep. Pramila Jayapal, D-Washington. CREW, a government ethics watchdog, filed a Freedom of Information Act request for documents that might detail Kelly's role in immigration policies that involved unaccompanied migrant children. CREW cited public reaction to CBS News' report in its request for the documents.

"There is a strong public interest in the requested documents. While in government, Kelly was directly involved in implementing the family separation policy, and he now works for a for-profit operator of child detention centers, Caliburn, that has reaped substantial financial benefits from that very policy," wrote CREW attorney Nikhel Sus. "The public has a compelling interest in learning whether Kelly was involved in any communications with or decisions concerning Caliburn or its related entities, both while he was in government and following his departure from the White House in January 2019."

But in the lawsuit filed in federal court against the U.S. Department of Health and Human Services (HHS), Sus wrote the request was rejected. HHS deemed the request for documents "fatally overbroad and burdensome," according to the lawsuit. Sus had requested documents that included references to Kelly and either the Homestead facility or the companies Kelly now works for.

Sus is asking a federal judge in the U.S. District Court for the District of Columbia to order HHS to immediately process his request and turn over its findings.

A CBS News request for comment made to HHS was not immediately returned. Caliburn declined to comment.