If a taxpayer has unpaid federal tax debts, the IRS typically offsets future refunds to pay down those debts. The statutory authority for the IRS to do this offset is §6402(a):
(a) General rule. In the case of any overpayment, the Secretary, within the applicable period of limitations, may credit the amount of such overpayment, including any interest allowed thereon, against any liability in respect of an internal revenue tax on the part of the person who made the overpayment and shall, subject to subsections (c), (d), (e), and (f), refund any balance to such person.
https://www.tomtalkstaxes.com/p/the-little-known-offset-bypass-refund (May 16, 2025)