The largest workers union at the Colombian coal mine Cerrejon walked out on strike on Monday, the group said, after its members voted overwhelmingly to support the move following a collapse in contract negotiations.
Some 99% of members of the Sintracarbon union who voted on possible strike action earlier this month backed the walkout over arbitration.
"Despite the union’s efforts to reach a negotiated agreement, we have determined to start the strike today from 03:15 in the afternoon," the union said in a statement.