"She did a disservice to her staff, to her colleagues, and while it is ultimately up to her constituents in California to be the final judge of her actions, I think it's safe to say that she did a disservice to the hardworking taxpayers from all corners of this country who expect and deserve more from their elected leaders," said Rep. Jo Bonner (R., Ala.), the committee chairman.
The embarrassing vote comes as Richardson faces a tough race to win reelection against fellow Democratic Rep. Janice Hahn in a newly drawn district.
The House chamber was nearly empty, despite the rare moment, as Ethics Committee members presented the charges, which included engaging in conduct that "brought discredit upon the House."
The reprimand was approved on a voice vote.
Rep. Charles W. Dent (R., Pa.), who oversaw the investigation, said that a disabled veteran who worked in Richardson's office as part of the Wounded Warrior Project wrote in a letter of resignation that the work environment was so hostile that she would "rather be at war in Afghanistan" than continue working for Richardson.
During the investigation, Bonner said, the committee heard "desperate, sometimes emotional, pleas for help" from Richardson staff members.
The committee's report said Richardson sought to influence the testimony of staff members before the Ethics Committee by suggesting they tell the committee their work on her campaign had been voluntary.
It said that in the fall of 2010, she directed a staff member to volunteer for her opponent's campaign under a fake name to gather information. It said the coercion of staff began in early 2010 and continued in the current campaign, even though Richardson knew she was under investigation.
The congresswoman, it said, had acted "with utter disdain" for the investigative process.
"I've never taken or threatened any action against any staffer who did not volunteer to work on my campaign," Richardson said Thursday. "There is no doubt that a number of staff felt compelled or coerced to do so. That was not my intent, and I deeply regret that this occurred."
Richardson, in a filing with the committee, said she accepted the punishment because ending the matter, rather than staging a fight that "would consume many more months and much more of her time and attention, is in the best interests of her constituents and of the House."
This article contains information from the Associated Press.