Workers at Chile’s Codelco copper mine are holding a nationwide 24-hour strike to protest modernization plans that union leaders say could lead to the loss of hundreds of jobs.

The work stoppage is the first in nearly 18 years at the state-owned mine. It involves workers at Codelco’s sites across the country, including at the mines of Chuquicamata, El Teniente and Andina.

Codelco, the world’s largest copper producer, is expected to lose at least 4,500 tons and more than $40 million by the strike action.

Union officials say modernization plans will lead to huge job losses and possible privatization at some of the plants.

Company officials say the plants will not be privatized.

The strike comes on the 40th anniversary of the nationalization of Chile’s copper mines, which led to the creation of Codelco.