Three Senate Democrats on Tuesday sent a letter to the Department of Homeland Security, asking for more information about the department’s purchase of 10 used jets for $464 million.

The department purchased those planes using a no-bid contract, saying it had no time to consider other sellers because the planes were needed urgently for deportation flights. Beginning in January, the department bought seven Boeing 737 passenger jets and three luxury business jets, all from Daedalus Aviation Corporation, a Northern Virginia company with no history as a federal contractor.

But, as The Times reported earlier this month, the department has barely used its new fleet. It has already sought to loan or lease two of the luxury jets to other agencies, and it has kept the passenger 737s idle for months at a time at an airport in Lake Charles, La.

In their letter, Senators Richard Blumenthal of Connecticut, Peter Welch of Vermont and Adam Schiff of California asked the department to provide records of communication between Daedalus and both current and former Homeland Security leaders.

The senators also asked for details about how often the planes had flown and who was on board. And they asked the department to explain why it had chosen Daedalus, which had no prior federal contracts of its own, though it had served as a subcontractor.

“The waste generated by parking most of these aircraft compounds the loss of taxpayer funds involved in the suspect, no-bid process the Department hurriedly implemented to buy these jets,” the senators wrote.

The Department of Homeland Security did not immediately respond to a request for comment about the letter. Earlier this month, the department told The Times that the purchase of the planes had been approved by the former Homeland Security secretary, Kristi Noem, whom President Trump fired in March. At the time, the department also said that two of the 10 planes would be used for deportation flights this month.