Union members at china clay company Imerys are to be balloted over possible strike action against planned job cuts.
China clay is also known as kaolin
The Transport and General Workers' Union said ballot papers would be issued this week and members had until mid-February to vote.
Imerys plans to axe 500 jobs in Devon and Cornwall when it relocates some of its operations to Brazil where costs are lower.
The company said that it was disappointed by the ballot decision.
Imerys is to close one of its seven china clay pits in the St Austell area.
One refinery and two drying units will also be closed in Cornwall; and a pit at Lee Moor - north of Plymouth in Devon - will also close, along with its refinery and drying unit.
Imerys is the largest employer in Cornwall, employing about 2,000 people.
The French-owned company said the cuts were necessary and would help ensure the future of the rest of its operations in the South West.
Unions claim the planned cuts will take £12m a year out of the local economy.
China clay, or kaolin, has a variety of uses, but is mainly used to whiten and give a glossy coating to paper.