D.C. Code § 47-1812.17

For the purpose of determining the liability of any person under this chapter and the extent of such liability, the Mayor may require the taxpayer to furnish the District with a true and correct copy of such person’s federal income tax return, and a copy of any federal partnership return with respect to any or all partnerships in which the taxpayer has a proprietary interest, for any taxable year, and a reconciliation of such return with the taxpayer’s District return for such taxable year.