Chilean port workers staged protests on Thursday, disrupting the loading and unloading of ships in one of the biggest exporters of raw materials from copper and lithium to pulp and fruit.

A planned 24-hour strike by members of the UPC and FTPC umbrella unions began around 8 a.m. local time. The Ventanas port confirmed activities undertaken by union members are suspended. Television images showed workers blocking roads near the biggest port of Valparaiso. Local media reported protests by stevedores in the town of Talcahuano.

The two unions are pushing authorities to take action over a series grievances including safety conditions and recent layoffs at coal-handling facilities associated with the shift away from thermal power.

To be sure, the stoppage was announced earlier this week, and workers are scheduled to resume activities on Friday. Still, the strike is being touted as a warning, with further protests possible. 

Copper producers including BHP Group, Codelco and Anglo American Plc didn’t immediately provide comment on any impact.