LONDON, April 30 (Reuters) - BHP Billiton , the world's largest mining company, said on Thursday that union blockades at its Cerro Matoso nickel operation had forced it to declare force majeure with some customers.
Unionised workers have been blocking access to the Cerro Matoso ferronickel mine and processing plant in Colombia since April 14 to protest a change to 12-hour shifts from eight previously.
Since last week, BHP has been flying some workers into the ferronickel plant with a hired helicopter in order to resume production, at least partially, despite the blockades that the company says are illegal.
"As a result of an illegal union work stoppage and blockade of its plant facilities at the Cerro Matoso operation, it is operating at less than full capacity," a company spokeswoman said in an emailed statement.
"As a result, and, as is normal practice, we have taken the prudent step of issuing force majeure notices to customers and the Colombian State Mining and Environmental Authorities."
"The company will continue to pursue a resolution of this matter, which relates to a change in work rosters within some business units, directly with the union and through legal avenues."
Cerro Matoso is one of the assets that form BHP's proposed spin-off company South32.
South32 is due to list on May 18, pending approval from BHP shareholders on May 6.
BHP said that it does not expect the current union blockade to have a material financial impact on BHP Billiton or South32. (Reporting by Silvia Antonioli and Eric Onstad; editing by Jane Merriman)