Cadbury workers are considering strike action over pay, according to union Unite.
The union claims Cadbury has broken the terms of a long-standing pay deal with workers at its Bourneville, Chirk, Marlbrook and Somerdale plants.
Around 1,300 staff are employed at the plants.
Ballot papers consulting on industrial action began to arrive at the homes of workers at the UK's best-known chocolate maker on Saturday. The ballot will run to 18 August.