House Oversight Chairman Darrell Issa is asking two top officials at the Department of Homeland Security to answer questions before his committee next week on their handling of freedom of information requests.

Mr. Issa’s investigators have been looking into allegations that DHS routinely delayed requests made by journalists and activists under the Freedom of Information Act. The investigators have had transcribed interviews with several department employees already, including ones who have said that political appointees interfered in the FOIA process.

Now Mr. Issa (R., Calif.) has requested that two political appointees — Mary Ellen Callahan, the department’s chief FOIA officer, and Ivan Fong, the department’s general counsel — appear at a hearing on Thursday, March 31 for what are likely to be tough questions, aides said.

Both are expected to appear voluntarily, and have not been issued subpoenas. The department’s assistant secretary for legislative affairs said earlier this month that officials had agreed to participate in hearings and that they have sent thousands of pages of documents to the committee.