Congress is investigating the District of Columbia's move to legalize marijuana and demanding documents showing how money has been spent to change the city's pot laws. 

Rep. Jason Chaffetz, a Utah Republican, sent a letter to Mayor Muriel Bowser late Tuesday asking her to reconsider moving forward with legalization. Chaffetz chairs the House Oversight Committee, which has authority over District government. 

District voters approved an initiative in November that legalizes possession of small amounts of pot for use in the home. Congress approved language in December that appeared to block the initiative, but District leaders argued they could still legalize pot because the initiative was enacted before Congress took action. 

Chaffetz says that interpretation is wrong and that legalizing pot on Thursday as Bowser plans would be clearly illegal.