The union representing workers at Chile’s Escondida copper mine, the world’s largest, said on Wednesday it was preparing for a lengthy strike if owner BHP did not drop a historically “awful” attitude towards its labor force to reach a “fair and equitable” deal in looming contract talks.

In its first written comments ahead of the talks due to start in June, the union said it was preparing a contract proposal to put to members. It said it was also building a contingency fund through extra levies paid by members to provide them with financial support in the event of a strike.