GPMU members at St Ives are stepping up pressure on the group with industrial action.
Staff at the Caerphilly plant will launch overtime bans and stoppages today (27 October). They are angry at proposed redundancies.
Action is ongoing at Peterborough and Andover after pay talks failed. Staff at Roche and Plymouth plants are also locked in talks.
GPMU deputy general secretary Tony Burke stressed it was industrial, not strike, action: "Hopefully they will get round the table and reach a sensible agreement with us," he said.
The union is also taking St Ives in Bradford and Bristol typesetter Wyvern 21 to the Central Arbitration Committee for ruling on union recognition rights.
"Some firms refuse to talk and are stuck in the 1980s with red braces and mobile phones the size of bricks," said Burke.
But it has won voluntary recognition at Field Boxmore's Bourne factory, MY Cartons in Gillingham, Rowpack Containers in Manchester and Maidstone Paper Company.
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