SANTIAGO, Sept 22 (Reuters) - Miners at Escondida, the world's biggest copper mine, began a 24-hour strike on Monday morning, the union told Reuters.
Workers did not board buses for the first shift, which is due to begin at 8 a.m. (1100 GMT), the union head, Patricio Tapia, said.
The union said last week it would hold two 24-hour stoppages as it seeks better working conditions.
Escondida is controlled by global miner BHP Billiton , and Rio Tinto also owns a 30 percent stake.
Reporting by Fabian Cambero, Writing by Rosalba O'Brien