Senate Judiciary Committee leaders are demanding that Apple provide a witness for an upcoming hearing on app stores and digital competition after the iPhone manufacturer has refused to participate, according to a new letter to the company released Friday.

In the letter addressed to Apple CEO Tim Cook, Sens. Amy Klobuchar (D-MN) and Mike Lee (R-UT) say the company “abruptly” decided not to provide a witness for an April hearing on digital markets focused on Apple’s App Store and the Google Play Store.

“Apple has been aware for weeks that the Subcommittee was planning a hearing on this topic and was engaged in discussions with our staff regarding who would testify on Apple’s behalf,” the senators wrote to Apple Friday. “Yet a little more than two weeks [16 days] before the planned hearing, Apple abruptly declared that it would not provide any witness to testify at a hearing in April.”

Apple did not immediately respond to a request for comment from The Verge Friday.

Apple’s App Store practices have been under intense scrutiny by lawmakers over the last year. In 2019, the House Judiciary Committee launched an investigation into competition in the tech industry, including Apple’s App Store. Throughout the probe, lawmakers homed in on the 30 percent fees Apple charges app developers. In a Verge interview last June, Chairman David Cicilline (D-RI) called the practice “highway robbery.”

The criticism extends to the app developers themselves. Fortnite publisher Epic Games sued Apple last year, accusing the company of violating US antitrust laws after it removed the popular battle royale game from the App Store. The trial is set to begin on May 3rd.

“Apple’s sudden change in course to refuse to provide a witness to testify before the Subcommittee on app store competition issues in April, when the company is clearly willing to discuss them in other public forums, is unacceptable,” the senators wrote. “We strongly urge Apple to reconsider its position and to provide a witness to testify before the Subcommittee in a timely manner.”