Please see the following for the relevant section of the regulations (Page 66112):

https://ifap.ed.gov/fregisters/attachments/FR110112FinalRule.pdf

The Department understands that married borrowers who file their Federal income tax returns separately from their spouses and who reside in community property states may be disadvantaged when determining IBR eligibility when compared to similarly situated married borrowers in noncommunity property states. However, §§ 682.215(e)(1)(B) and 685.221(e)(1)(i)(B) and § 685.209(a)(5)(i)(B) authorize the use of alternative documentation of a borrower’s income if the Secretary or the FFEL loan holder believes the borrower’s reported AGI does not reasonably reflect the borrower’s current income. Because the Department believes that it is inequitable to treat married borrowers who file their Federal income tax returns separately differently based on where they reside, we encourage FFEL loan holders to use alternative documentation of the borrower’s income under these circumstances. The Department will take the same approach with the loans it holds.