U.S. Rep. Raul Grijalva is one of 60 Democrats taking part in a sit-in on the House floor Wednesday.
A representative from Grijalva's office confirmed his participation. Grijalva, 68, has served in the House since 2003.
The group is protesting Congress's inaction in gun control.
The Senate rejected four gun control measures Monday following the June 12 shooting deaths of 49 people in a massacre inside an Orlando nightclub.