CBP officials knew of 'inappropriate' online posts as far back as February 2018 One Facebook group is currently under CBP investigation.

The agency said on Monday it has launched an investigation into a Facebook group known as “I’m 10-15,” after the account was revealed in a report by ProPublica. On Friday, the agency added that it was made aware of additional social media posts also alleged to have been posted by its personnel.

The developments come as the agency’s leadership is under fire for allowing what Democrats say is a toxic culture to fester at Border Patrol stations, where agents are overwhelmed and under resourced.

“Too much of CBP has been an out of control agency for too long and it must be reined in immediately,” said Senate Democratic Leader Chuck Schumer, D-New York, said earlier this week.

The 2018 memo, released Friday by CBP, suggests agency leaders have known for a while that employees were potentially violating codes of conduct while on social media.

In an all-hands memo sent to agency employees on Feb. 8, 2018, Matthew Klein, CBP’s assistant commissioner of the Office of Professional Responsibility wrote, that the agency “was made aware of a private Facebook group page that only a specific group of CBP employees could access, on which inappropriate and offensive posts were made.”

Klein did not elaborate on the nature of the posts.

"The bottom line is the Agency may bring discipline against an employee who posts offensive messages on a social media page where there is nexus to the Agency workplace,” he added.

It is not clear whether the Facebook group referenced in the 2018 memo is the same exposed by ProPublica and currently under investigation by the Homeland Security Department’s inspector general’s office.

CNN reported Friday that a second group had been uncovered, although it had not confirmed that government personnel were involved.

A CBP spokesperson said Friday that new screenshots have been passed along to its office that it would investigate potential employee misconduct.

The agency’s Office of Professional Responsibility, led by Klein, "is investigating the posts to determine the facts," a spokesperson said in a statement.

Recent posts within one secret group were aimed at Democratic lawmakers, including Rep. Joaquin Castro and Rep. Alexandria Ocasio-Cortez, ahead of their visits on Monday to El Paso and Clint, Texas, to tour CBP's detention facilities.

Castro, the chairman of the Congressional Hispanic Caucus, called the Facebook posts "disgusting and vile" and said that many agency employees "have become desensitized to the point of being dangerous to the migrants in their care."

Castro, whose twin brother Julián Castro is a Democratic candidate for president, has called for a congressional investigation into the matter,

"This isn't about 'a few bad eggs.' This is a violent culture," Ocasio-Cortez, who was the target of numerous posts, wrote on Twitter on Monday. "How on earth can CBP's culture be trusted to care for refugees humanely?"

A CBP spokesperson said in the statement on Friday that the posts don't reflect the agency's values.

"If the investigation verifies that employees posted content in violation of CBP’s code of conduct, the findings will inform management decisions regarding appropriate disciplinary action," the statement said.

ABC News' Soorin Kim contributed to this report.