A group of Democratic senators says United Airlines hasn’t responded to their questions about an incident earlier this month in which a passenger was forcibly removed from a flight after refusing to give up his seat for crew members.

“I am disappointed and troubled that United Airlines has so far failed to answer basic questions about the troubling incident aboard Flight 3411,” said Sen. Maggie Hassan (D-N.H.) “No passenger should ever experience the mistreatment that we all saw on that United flight. I will continue to use all of the tools at my disposal, including introducing new legislation later this week, to help prevent such an incident from happening again and to strengthen consumer protections for the flying public.”

After video surfaced of David Dao, 69, being pulled from his seat by aviation security officers, a group of senators led by Hassan, Brian Schatz (D-Hawaii), Richard J. Durbin (D-Ill.) and Charles E. Schumer (D-NY) sent a letter to United chief executive Oscar Munoz demanding a more detailed account of what happened on the plane and a clearer understanding of the airline’s policy on removing ticketed passengers after they’ve boarded a  flight.

They gave the airline until Apr. 24 to respond, but have heard nothing. Officials at United did not respond directly to questions about when they will respond to Hassan and Schatz’s letter but emailed a statement outlining some of the actions they have taken.

“United Airlines continues to focus on making this right, as no one should ever be mistreated this way,” the airline said in the statement. “As part of our commitment to our customers, we are in the process of conducting a thorough review of our policies. We have already committed we will not ask law enforcement officers to remove passengers from our flights unless it is a matter of safety and security.  Second, we issued an updated policy to make sure crews traveling on our aircraft are booked at least 60 minutes prior to departure.”

Hassan and Schatz are expected to introduce legislation this week designed to prevent future incidents like the one that took place on United flight 3411. The goal is to strengthen protections for passengers. Other legislators have also indicated they plan to introduce legislation in the wake of the Apr. 9 incident.

Also signing the letter were Sens. Edward J. Markey (D-Mass.), Chris Van Hollen (D-Md.), Ron Wyden (D-Ore.), Richard Blumenthal (D-Conn.), Tammy Baldwin (D-MN), Robert P. Casey Jr. (D-PA), Amy Klobuchar (D-Minn.), Al Franken (D-Minn.), Catherine Cortez Masto (D-Nev.), Cory Booker (D-N.J.), Mazie K. Hirono (D-Hawaii), Tammy Duckworth (D-Ill.), Tom Udall (D-N.M.), Mark R. Warner (D-Va.), Robert Menendez (D-N.J.), Sherrod Brown (D-Ohio), and Jack Reed (D-R.I.).

Senate Democrats aren’t the only officials frustrated by the lack of information from the airline.

United and the Chicago Department of Aviation also failed to meet an April 20 deadline to respond to questions from the leaders of the Senate Commerce Committee.

In a letter sent to leaders of the Senate’s Commerce, Science and Transportation Committee and the Subcommittee on Aviation Operations, Safety and Security, Munoz outlined concrete actions the airline has taken in light of the dragging incident. He said they will provide answers no later than April 27 — just three days before Munoz pledged to publicly release the results of an internal investigation.

Likewise, Ginger S. Evans, head of the Chicago Department of Aviation, which manages O’Hare, and the three officers involved in the April 9 incident, asked for an extension until April 26, “ … in order to ensure the completeness of our response.”

Committee members were not happy with the request.

“We’re disappointed that neither United Airlines nor the Chicago Department of Aviation has yet provided substantive answers to the straightforward questions we asked about the forcible removal of a passenger on April 9, 2017,” wrote Sens. John Thune (R-S.D.), Bill Nelson (D-Fla.), Roy Blunt (R-Mo.) and Maria Cantwell (D-Wash.) “Getting answers for the public about what happened and what can be done to prevent such an incident from happening again is a priority for the members of our committee. We find any further delay in getting necessary answers unacceptable.”