After re-opening operations on Oct. 17, the IRS said in an email to tax professionals Friday that its employees are reporting back to work, and the agency is assessing the impact of the 16-day shutdown on its national operations.

“At this point, we know we received a large amount of correspondence during the closure,” the IRS said on its Web site. “We know there will be a substantial increase in demand for our phone services and many other operations. On Oct. 17, we started reopening our phone lines and our Taxpayer Assistance Centers, both of which will take time to ramp up to normal operating status. In addition, other business operations have started resuming, including the processing of billions of dollars of refunds for individuals and businesses and honoring transcript and authorization requests from third parties.”

Given the high demand for services, the IRS said it is encouraging taxpayers to wait to call or visit if their issue is not urgent, and to continue to use automated applications on the IRS website, www.IRS.gov, whenever possible.

Taxpayers who need immediate assistance are being encouraged to visit Taxpayer Assistance Centers in their area or try call centers but should be aware there will be delays. The IRS also has delayed the start of its 2014 renewal season for tax preparers to apply for their Preparer Tax Identification Numbers, or PTINs (see IRS Delays PTINs for 2014).

“In the days ahead, we will continue assessing the effect of this unprecedented situation on IRS operations, and we will do everything we can to resume our normal operations as quickly as possible so that we can best serve the needs of the American taxpayer,” the IRS added. “We greatly appreciate the patience of taxpayers and tax professionals during this period.”