The Department of Justice has launched a criminal investigation into the Southern Poverty Law Center (SPLC), a prominent civil rights organization, the group’s CEO said on Tuesday.

Bryan Fair, the CEO of the SPLC, said the details of the investigation were not entirely clear, though “the focus appears to be on the SPLC’s prior use of paid confidential informants to gather credible intelligence on extremely violent groups”.

The investigation is being handled by the US attorney district for the middle district of Alabama, which includes Montgomery, the state capital where the SPLC is based, according to a person familiar with the matter. The justice department and the US attorney’s office for the middle district of Alabama did not respond to a request for comment.

Fair said the group used to use paid informants to infiltrate extremist groups and monitor them, but no longer does.

“This use of informants was necessary because we are no stranger to threats of violence. In 1983, our offices were firebombed, and in the years since, there have been countless credible threats against our staff,” he said. “For decades, we engaged in unprecedented litigation to dismantle the Klan and other hate groups. In light of that work, we sought to protect the safety of our staff and the public.”

The investigation comes as the Trump administration has pledged to crack down on non-profit groups opposed to its priorities. Conservative groups have long decried the way the SPLC has labelled certain right-leaning groups as “hate groups”.

Last year, the FBI announced it was ending its relationship with the organization, saying the organization had defamed right-leaning groups by labelling them hate groups.

“Today, the federal government has been weaponized to dismantle the rights of our nation’s most vulnerable people and any organization like ours that stands in the breach,” Fair said. “We will vigorously defend ourselves, our staff, and our work; we will continue to fight hate; and we will continue to seek a safer and more just world.”