(ANSA) - Cagliari, September 12 - Leaders from two labor unions on Wednesday climbed 70 meters to the top of silos at the threatened Alcoa aluminum plant in Sardinia. "They reneged on everything," said Franco Bardi, the regional boss of FIOM CGIL, who announced the protest after a heated meeting with the company. Last week workers ascended the same silos in protest over plans by the American aluminium giant to shut down a smelter and put hundreds of jobs at risk. The other labor leader to climb the silo Wednesday was Rino Barca, regional boss of FIM CISL. On Monday a demonstration in Rome turned violent and 15 people were injured in clashes between workers and the police. Talks between the government, unions and Alcoa have been aimed at finding a way to save the unprofitable plant by finding a buyer willing to take it on. However, Industry Minister Corrado Passera has described the challenge of keeping the factory open as "almost impossible".