In a blistering 17-page letter, the head of a congressional committee on Friday accused federal officials of improperly withholding information on Border Patrol agents’ misconduct in a secret Facebook group from congressional investigators.

Rep. Carolyn B. Maloney, chair of the House Committee on Oversight and Reform, said in the letter that she plans to subpoena internal Border Patrol documents detailing misconduct related to the Facebook group, which included some 9,500 current and former agents. First exposed by ProPublica in July 2019, the social media community called “I’m 10-15” was rife with dehumanizing and misogynistic postings, including an image of President Donald Trump sexually assaulting Democratic Rep. Alexandria Ocasio-Cortez.

The dispute that prompted Maloney’s letter centers on the refusal of the Border Patrol’s parent organization, Customs and Border Protection, to turn over documents identifying by name, rank .and geographic location the agents who were disciplined or fired for making offensive posts in the Facebook group. CBP has also failed to provide congressional investigators with any details about specific incidents that led to agents being punished or fired. The records that CBP has provided to the committee are heavily redacted, according to Maloney.

“While I did not come to the decision to subpoena the CBP lightly, it is necessary,” said Maloney, a New York Democrat, in a statement to ProPublica. “The Committee needs these unredacted documents to oversee whether CBP is properly disciplining its employees and whether employees who CBP found to have committed misconduct are still working directly with immigrant women, children, and babies.”

CBP has long insisted that it is barred by federal law from disclosing key details about its disciplinary process, including the names of employees who’ve faced discipline for violating the agency’s policies.

In the letter, however, Maloney called CBP’s refusal to turn over the unredacted disciplinary records as “legally baseless” and asserted that her committee “has direct jurisdiction over federal employees and agency disciplinary procedures.”

CBP has said publicly that it investigated 136 employees in connection to the “I’m 10-15” group and another Facebook group, and that the probe led to the firing of four agents and the suspension of more than three dozen others. Still, the agency has kept most other facts about the investigation confidential, declining to share information with the committee or issue a public report.

“To date, CBP has provided a significant volume of documents on the matter, some of which were publicly released by the Committee without CBP’s consent, in addition to providing numerous briefings on the matter,” a CBP official said in an emailed statement. “Since the beginning of this investigation, CBP’s primary goal has been to provide transparency while still protecting the health and safety of our personnel, given the high degree of social unrest and the potential hostile targeting of employees for the nature of their employment.” The official said the agency is aware of Maloney’s intent to subpoena the documents.

Her letter states that the documents CBP has already turned over show that the agency “reduced penalties for numerous employees” who engaged in misconduct; three agents who were slated to be fired had their punishments reduced to suspensions from work, while 19 others had the length of their suspensions cut down.

The committee is seeking further information about an agent identified only as “Fired Agent #1” in the letter. ProPublica’s reporting indicates that this is Thomas Hendricks, who served as a supervisory agent in Calexico, California, until he was ousted from the Border Patrol in October 2019 because of his offensive posts in the Facebook group. It was Hendricks who posted the image of Ocasio-Cortez being assaulted.

According to Maloney’s letter, Hendricks told internal affairs investigators that his postings were “just having fun” and later described them as “good natured.”

Hendricks appealed his firing, but in a decision handed down last month a federal appeals board denied his request to be reinstated. The decision shows that the agent made offensive Facebook posts demeaning women and gay men while working. “It’s not a big deal to post a meme on duty,” Hendricks told investigators.

His attorney, Joel Kirkpatrick, did not return requests for comment.