A new law enacted by Congress will require the IRS to show its calculations when alleging that a taxpayer’s returns have an error, or that their tax liability has changed.

The law, known as the Internal Revenue Service Math and Taxpayer Help Act, mandates that the agency, when notifying taxpayers of an error, provide a clear description of the error, a detailed breakdown of the mathematical calculations to correct the error, and procedures to cure that error. Leaders in Congress presently allege that the agency does not do so, leading to many taxpayer difficulties when faced with a notice of an error that requires them to pay more taxes to the government.

“Americans must show the math on their tax return, and now the IRS has to as well. Instead of having to take the word of the federal government’s most feared agency, taxpayers will have the information to successfully challenge the IRS,” Rep. Jason Smith (R-Mo.), chairman of the House Ways and Means Committee, which has jurisdiction over all tax-related matters in the House, said in an emailed statement about the bill.

President Donald Trump signed the bill into law on Nov. 25. 

“For too long, the IRS has caused headaches and confusion when a taxpayer makes a fixable mistake on their taxes, providing no explanation as to why a refund is different than expected, or how to correct an error,” Rep. Randy Feenstra (R-Iowa), the bill’s lead sponsor, said in the same statement.

“This law will require the IRS to clearly communicate tax-filing errors to Iowans and help them not only understand the mistake but also challenge it if they see fit.”

The bill was unanimously passed by the House and Senate, and is one of the few bills that have received no opposition from either Democrats or Republicans during the 119th Congress.

The U.S. Congress’s Joint Committee on Taxation, one of the few joint committees of both the Senate and House, estimated that the bill would reduce the government’s revenues by $38 million over a 10-year period until 2035.

In 2014, the agency published a “Taxpayer Bill of Rights,” which sets out obligations of the agency to taxpayers. Generally, when the IRS assesses an error, a taxpayer has 60 days to dispute it.