Seven people were wounded Wednesday in a gunbattle between rival factions of Argentina's Uocra national construction union.
More than 50 people were arrested after the clash in the capital suburb of Florencia Varela, where several vehicles were set on fire.
The violence began when people from one of the contending factions burst into the local Uocra union hall during a meeting, witnesses said.
One of the nine Uocra delegates shot in a similar confrontation in Florencio Varela six months ago was left a paraplegic.
Seven people were wounded last week in a clash between rival Uocra factions in the remote southern city of Ushuaia.
Shootouts have become all too common in intra- and inter-union conflicts in Argentina and several officials of the railway union are currently on trial for the fatal shooting of a young activist in 2010.
Police are now investigating the abduction and beating of a key witness in that case. EFE