The Meat Workers Union says employees at all eight AFFCO plants have voted overwhelmingly in favour of siding with their locked-out colleagues, despite lockout notices being lifted by the company.
Strike action has been taking place since the end of February this year as the parties battle over a collective contract.
The Employment Relations Authority has agreed to mediate in the long-running dispute, but meanwhile the union has recommended to workers that they continue with industrial action.
AFFCO lifted lockout notices from Wednesday morning on about 300 workers mainly at the Feilding and Whanganui meat processing plants, but 450 remain locked out.
Union spokesperson Dave Eastlake says secret ballots at all eight sites on Wednesday afternoon came back overwhelmingly in favour of continuing strike action until all staff are allowed back to work.
"People have had a long row to hoe and they're certainly suffering some hardship, but they're not prepared to have a split in their ranks. That's the way they voted, they had their say and that's the result."
Mr Eastlake says the Employment Relations Authority could announce a date for a hearing on Thursday and further mediation is planned for Monday, so he hopes AFFCO will lift the lockout for all workers in the meantime.
AFFCO meanwhile says the union has rejected its goodwill offer to lift the lockout on all workers progressively.
Operations manager Rowan Ogg says the company had provided a timeline of two to three weeks to withdraw the lockout on all union members, but wanted a demonstration of goodwill, such as the lifting of the strike notice. Mr Ogg says the union refused.
The Employment Relations Authority has not yet set a date for facilitation, which is only available to parties having serious difficulties in collective bargaining.
It is the highest form of government-assisted mediation available and is non-binding.