The lawmaker, Domingo Alcibia, had fled after the video's appearance but was arrested in a small town outside of Sucre, the capital of Chuquisaca province, where feminists have been picketing the prosecutor's office demanding that Alcibia be prosecuted for rape.
Alcibia faces charges of abuse of power, but is not being prosecuted for sexual assault because the woman, a janitor, did not file a complaint, according to the prosecutor in charge of the case, Fernando Pacheco.
The video was taken by a security camera after a Christmas party on Dec. 20, and was broadcast on local television and posted to YouTube last week.
It shows the woman, who has not been identified by name, being brought into the room in the provincial legislature by others, stumbling and falling. She is placed in a chair, apparently unconscious.
Alcibia, drunk, enters the room, turns off the lights, lowering the already blurry video quality. He places the woman on the floor, unfastens his belt and appears to have sex with her.
The lights come back on a few minutes later and Alcibia jumps off the woman. He pulls up his pants and puts her back in the chair, and others later enter the room to check on her.
When the incident came to light last week, Alcibia, a member of President Evo Morales' governing MAS bloc, said he didn't remember anything because he was drunk but denied that he had sexually assaulted the woman.
Local TV stations ran the video—it was unclear how they obtained it—and someone uploaded it to YouTube, which initially removed it but reinstated it on Tuesday given its news value, apparently after a query from The Associated Press.
YouTube normally removes videos with graphic or sexually explicit content but takes exception when they have "documentary, or news value," a company spokesperson said.
In such cases, YouTube posts "warnings and age restrictions" to safeguard users, said the spokesperson, who refused to be further identified in keeping with company policy. YouTube does not comment on individual videos.
After the scandal broke last week, Morales deemed "unacceptable" the behavior of Alcibia and another regional lawmaker who is seen at a different moment in the video making advances on another woman.
That lawmaker, Javier Humala, is also being charged with abuse of power, said Pacheco.
If convicted, each faces up to eight years in prison. Both men, ethnic Quechuas, were also expelled from MAS.
The U.N. and Bolivia's public ombudsman's office have both called for a rapid and impartial investigation of the case.
Associated Press Writer Frank Bajak contributed to this report from Lima, Peru