D.C. Mun. Regs. tit. 9, r. 9-115
The tax deducted and withheld at the source upon wages under the provisions of § 8(b) and § 8(c) of Title 12 of the Act shall be allowable as a credit against the tax imposed by § 3 of Title 6 of the Act upon the recipient of the income.
The credit set forth in § 115.1 shall be allowed against the tax imposed by § 3 of Title 6 of the Act for the taxable year of the recipient of the income which begins in that calendar year; Provided, that credit may be denied unless supporting Form D-2 withholding statements are furnished to the Deputy Chief Financial Officer.
If the recipient of income has more than one taxable year beginning in that calendar year, the credit shall be allowed against the tax for the last taxable year so beginning.
If the tax has been withheld at the source by an employer outside the District, credit or refund may be denied to the employee until that tax has been paid over to the Deputy Chief Financial Officer by the employer.
D.C. Mun. Regs. tit. 9, r. 9-115