Union officials have expressed anger at china clay company Imerys' decision to buy ceramics manufacturer UCM while its employees are facing redundancy.
Members are being balloted over possible strike action
British firm UCM has agreed to a takeover by Imerys for about £20.3m.
Imerys plans to axe 500 jobs in Devon and Cornwall when some operations are relocated to Brazil for lower costs.
The Transport and General Workers' Union (T&G) said it showed the firm's "duplicity" towards its workforce. Imerys was unavailable for comment.
Jennie Formby, T&G national secretary, said Imerys had told the union it could not afford to make higher payments to those facing redundancy after up to 40 years of service because of substantial losses in recent years.
She said: "To our members facing redundancy and bleak job prospects it means Imerys is paying over the odds and has misled them by saying there is no money for a decent pay-off."
The T&G is balloting about 900 members from Devon and Cornwall over possible strike action against planned job cuts.
Members have until mid-February to vote. The company has expressed disappointment at the ballot decision.
Imerys is the biggest 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.
The company is the world's largest producer of china clay, operating in 250 locations in 43 countries.
China clay, or kaolin, has a variety of uses, but is mainly used to whiten and give a glossy coating to paper.