26 CFR §1.6015-4

1. (a)A requesting spouse who files a joint return for which a liability remains unpaid and who does not qualify for full relief under § 1.6015-2 or 1.6015-3 may request equitable relief under this section. The Internal Revenue Service has the discretion to grant equitable relief from joint and several liability to a requesting spouse when, considering all of the facts and circumstances, it would be inequitable to hold the requesting spouse jointly and severally liable.
2. (b)This section may not be used to circumvent the limitation of § 1.6015-3(c)(1) (i.e., no refunds under § 1.6015-3). Therefore, relief is not available under this section to obtain a refund of liabilities already paid, for which the requesting spouse would otherwise qualify for relief under § 1.6015-3.
3. (c)For guidance concerning the criteria to be used in determining whether it is inequitable to hold a requesting spouse jointly and severally liable under this section, see Rev. Proc. 2000-15 (2000-1 C.B. 447), or other guidance published by the Treasury and IRS (see § 601.601(d)(2) of this chapter).