The Internal Revenue Service said it had resolved a computer system outage and is again accepting electronically filed tax returns.
In a statement released on Thursday, the agency said it had resumed processing individual and business tax returns, a day after a "hardware failure" forced the shutdown of several tax processing systems, including the e-file system.
IRS Commissioner John Koskinen said taxpayers should see little, if any, impact on their returns or refunds. Koskinen said employees worked through the night to get the system back online and he apologized for the inconvenience.
The agency said taxpayers do not have to take any additional action due to the outage, even those who filed returns electronically before or after the computer problems.
On Wednesday, Matt Leas, an IRS spokesman, had said a "power or electrical issue" caused the failures.
He provided no additional details.
Meanwhile, the IRS warned about tax scams involving the Affordable Care Act and penalties imposed under the law on people who go without health insurance.
In some cases, the agency said, unscrupulous tax preparers were telling clients to pay the penalties directly to them, and the they kept the money.