Senior legal adviser to the State Department Harold Koh resigned last week in protest of President Biden's continued use of the Trump-era policy Title 42, calling it "illegal" and "inhumane."

Koh wrote in his Oct. 2 resignation letter that the use of Title 42 "raises significant concerns about whether the United States is living up to its binding obligations under international law," according to Politico, which first reported the resignation.

In his letter, Koh wrote of how he has spent his legal career ensuring that the U.S. abides by its obligations under the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment (CAT), a U.N.-reviewed human rights treaty of which the U.S. is a signatory.

Koh wrote that he believes that Title 42 violates an article of CAT that prohibits a country from returning a person to a state where they have "substantial grounds for believing he would be in danger of being subjected to torture.”

Under Title 42, migrants can be deported without allowing for asylum during public health emergencies. The Trump administration used an interpretation of this to expel migrants at the border, citing the risk of spreading COVID-19. The Biden administration has recently implemented this policy to deport thousands of Haitians who had crossed into the U.S. from Mexico.

"I believe this Administration’s current implementation of the Title 42 authority continues to violate our legal obligation not to expel or return ('refouler') individuals who fear persecution, death, or torture, especially migrants fleeing from Haiti," Koh wrote.

In the past few months, Haiti has been shocked by a presidential assassination and a 7.2 magnitude earthquake.

Koh served as a legal adviser to the State Department from June 2009 to January 2013 under the Obama administration. He also previously served as assistant secretary of State for Democracy, Human Rights, and Labor from 1998 to 2001 under former President Clinton.

One source told Politico that Koh would be staying on at the department in a consulting role.

Asked about the letter during Monday’s briefing, White House press secretary Jen Psaki said she hadn’t seen it but reiterated that Title 42 is a public health authority in place due to the ongoing coronavirus pandemic.

“We don’t see Title 42 as an immigration policy. It is a public health authority because we are still in the middle of a pandemic and it is determined by the CDC,” Psaki said, referring to the Centers for Disease Control and Prevention. 

She noted that there are “several exceptions” to the rule, including for those who are fleeing persecution. 

The Hill has reached out to Koh and the State Department for further comment.

Koh's resignation comes shortly after U.S. Special Envoy to Haiti Daniel Foote resigned in protest to what he called the “inhumane, counterproductive decision to deport thousands of Haitian refugees."

"Our policy approach to Haiti remains deeply flawed, and my recommendations have been ignored and dismissed, when not edited to project a narrative different from my own,” wrote Foote.

Last week, Juan Gonzalez, senior director for the Western Hemisphere for the U.S. National Security Council, apologized for how the U.S. had treated Haitian migrants while he was visiting Haiti.

“I want to say that it was an injustice, that it was wrong,” Gonzalez reportedly said. “The proud people of Haiti and any migrant deserve to be treated with dignity.”

Updated at 4:48 p.m.