The IRS announced this over the weekend: (see also link below)
Take away: Don't confuse this with a full operational shutdown. The IRS is otherwise in as high gear as possible at the current time.
"In response to the national emergency and to protect our employees, America’s taxpayers, communities and our partners, the IRS has temporarily closed all Taxpayer Assistance Centers and discontinued face-to-face service throughout the country until further notice. The IRS is continuing to process tax returns, issue refunds and help taxpayers to the greatest extent possible. Click here for more info on taxpayer assistance center closures."
"The IRS is continuing to process tax returns, issue refunds and help taxpayers to the greatest extent possible. Taxpayers are highly encouraged to go to IRS.gov and to the newly created IRS.gov/coronavirus webpage where they can find the latest updates about IRS services, explore free options to file or request an extension to file at www.IRS.gov/freefile, find forms, tax help, refund status and payment options."