A group of 40 House Democrats have described “grave concerns” over the Trump administration’s secretive program of deportation flights and demanded the Federal Aviation Administration (FAA) address allegations of mistreatment and inhumane conditions on ICE charter jets.

In a letter shared with the Guardian and addressed to the FAA administrator, Bryan Bedford, the lawmakers describe the “urgent need for transparency” over ICE’s expanded use of commercial airliners to transfer detained immigrants and its “inappropriate and dangerous” efforts to shield these flights from public scrutiny.

“Credible reports indicate that individuals have been placed on flights without notice to counsel or family members, effectively disappearing from public view when flights are inappropriately shielded from tracking systems,” the letter states. “Families are left searching for their loved ones, and attorneys are denied meaningful opportunities to intervene, raising serious due process concerns.”