ADVERTISEMENT Economists say that the shutdown, which will pass its one-month mark next week, is starting to eat into economic growth. The White House has itself doubled its estimate on how much the shutdown is costing the economy, projecting that it would reduce quarterly economic growth by 0.13 percentage points each week it lasts.

Mnuchin was scheduled to lead a U.S. delegation to the World Economic Forum in Davos, Switzerland, between Jan. 22 and 25. The White House announced Tuesday a scaled-down delegation for the trip due to the shutdown, but Mnuchin was still listed as leading the group. While next week's hearing is meant to cover a broad range of implications from the shutdown, Neal specifically cited concern over how the IRS would function as tax filing season gets underway on Jan. 28.

More than 70,000 furloughed IRS and Treasury workers had missed a paycheck, he noted. This week, the IRS released a contingency plan to allow 46,000 workers to return to work without pay to deal with tax filings if the shutdown does not end.

The plan has not eased concern that the IRS will be able to function as needed and get tax refunds back to the American public and business sector on time.

The letter comes a day after IRS Commissioner Charles Rettig was meant to brief lawmakers on the issue. Neal said that he “cancelled.” House Democrats were reportedly unhappy with Treasury’s suggestion that a lower-ranking official be sent to brief them.

Updated: 3:22 p.m.