D.C. Code § 1-620.33
Any District government employee who operates a motor vehicle in the performance of his or her employment within the District of Columbia shall be deemed to have given his or her consent, subject to the conditions in this subchapter, to the testing of the employee's urine or breath for the purpose of determining drug or alcohol content whenever a supervisor has probable cause or a police officer arrests such person for a violation of the law and has reasonable grounds to believe such person to have been operating or in physical control of a motor vehicle within the District while that person is intoxicated as defined by § 50-2206.01(9), or while under the influence of an intoxicating liquor or any drug or combination thereof, or while that person's ability to operate a motor vehicle is impaired by the consumption of intoxicating liquor.
D.C. Code § 1-620.33