FILE PHOTO: U.S. Internal Revenue Services (IRS) employees rally in front of the Federal Building against the ongoing U.S. federal government shutdown, in Ogden, Utah, U.S., January 10, 2019. REUTERS/George Frey/File Photo

WASHINGTON (Reuters) - Thousands of Internal Revenue Source employees ordered to return to their jobs unpaid in order to handle the tax filing season are not showing up to work, the Washington Post reported on Friday, citing House of Representatives aides, as the partial federal government shutdown ground on in its 35th day.

President Donald Trump’s administration had called back 26,000 workers to the IRS division that includes the tax processing centers and call centers. About 9,000 workers could not be reached and about 5,000 more claimed a hardship exemption as of Tuesday, IRS officials have told members of Congress.

Reuters could not immediately verify the report.