The breakdown in negotiations increases the chances of a labour disruption -- that could happen as early as Sunday.
On Friday workers from three negotiating units voted down what the company called its final offer.
The union says talks resumed at 9 a.m. this morning but quickly broke down.
Union officials already have a strike mandate in hand and are warning that a work stoppage could be imminent.
The Alma facility hosts one of the company's (NYSE:RIO) most important North American aluminum smelters, with about 800 employees.