Americans who paid certain IRS penalties or interest during the COVID-19 pandemic could still be eligible for refunds, but Friday is the deadline to file claims.

The deadline follows a federal court's ruling in Kwong v. United States, which held that the government's COVID-era filing extensions may also have delayed when the agency could legally assess certain penalties and interest.

That means taxpayers who paid those charges during the affected period could be entitled to recover some of that money — but only if they file a claim on or before July 10.

While the potential impact is unclear, some experts say it could be significant.

"I would suspect it's a pretty big number. This happens to millions of people annually," Nathan Goldman, an accounting professor at North Carolina State University, previously told the New York Post.

According to the Taxpayer Advocate Service, taxpayers may qualify if they:

• Filed a return during the COVID-19 disaster relief period and were assessed penalties or interest.
• Paid or still owe penalties or interest for filing or paying taxes late during that period.
• Filed late international information returns.
• Missed a refund, refundable credit, withholding credit, estimated tax payment credit, or another tax benefit for tax years affected by the COVID-19 relief period.

The time frame generally covers Jan. 20, 2020, through July 10, 2023, though some claims involving tax years 2019 through 2022 may also qualify.

Filing a claim does not guarantee a refund. The IRS may approve or deny the request or not respond to the claim.

If a claim is approved, taxpayers could receive a refund for amounts already paid or have an outstanding tax balance reduced.

If the IRS denies the claim, taxpayers may challenge the decision or file a refund lawsuit. Under the Kwong ruling, taxpayers may seek relief in court if the IRS does not respond within six months.

Experts told the Post that taxpayers may preserve their right to pursue a refund by filing a protective claim with the IRS, which keeps the claim valid even if the case is held up by litigation.

The IRS recently began allowing eligible taxpayers to file Form 843 electronically through an online IRS account. Those who prefer to submit a paper claim should mail Form 843 to:

Internal Revenue Service

1973 N. Rulon White Blvd.

Ogden, UT 84201

Taxpayers filing by mail should write "Kwong v. United States" across the top of the form to identify the claim.

Tax professionals recommend reviewing individual circumstances before filing, as eligibility depends on each taxpayer's situation.