Cops cuffed Rosario Dawson and hauled her away from the Democracy Spring rally in Washington, D.C. 

The actress was among a group of about a dozen people who crossed a police line and then sat down in protest. It's unclear what Rosario was booked for, but cops say about 100 people were arrested Friday ... mostly for crowding or obstructing.

The Democracy Spring rallies have been going on all week in D.C. to protest all sorts of causes.

Rosario was with a group protesting the corruption of big money in politics.