A budget spat erupted into fisticuffs Wednesday when opposition legislator Graciela Camano punched fellow lawmaker Carlos Kunkel in the mouth.
Two television news channels broadcast the melee live as Camano got out of her chair to confront Kunkel during a session of the Upper House's constitutional affairs commission.
The two exchanged words, Kunkel gestured with his arms and Camano socked him then left the chamber.
"Under no circumstances will I allow Kunkel or anyone else to lack respect," Camano said later. "He wore me out because I have been putting up with him all year long. He kept shouting without making a single proposal."
She declined to reveal what Kunkel said, but added: "He is always attacking me."
Kunkel, a close ally of President Cristina Fernandez, did not immediately comment. Under congressional rules, he can file a complaint that could lead to possible sanctions against Camano.
Congress has been especially tense recently, with opposition lawmakers saying Fernandez's government is exerting tremendous pressure on them to vote for the 2011 budget.