Zambia’s mineworkers union said it opposes Vale’s $400m investment plan for the development of a copper mine at Konkola North.

Mineworkers Union of Zambia president Rayford Mbulu said the union is concerned about the treatment of workers by Vale, reports Bloomberg.

The Konkola North mine, being developed with African Rainbow Minerals and operated by Vedanta Resources, is scheduled to start production in 2013.

The copper mine’s initial output is estimated at 50,000t a year, which will later be expanded to 100,000t.