Meat processing company AFFCO and the Meatworkers Union have again failed to agree on a new employment contract.
The mediation talks concluded on Tuesday night.
Industrial action has been going on for two months as the two sides try to negotiate a new collective contract.
AFFCO has locked out up to 900 workers, but on Tuesday lifted a lockout notice allowing 300 to return to work on Wednesday.
Union national secretary Dave Eastlake says those workers, most of whom are from the Feilding and Whanganui plants, will probably go on strike alongside their colleagues.
"The indications we have are that very few, if any, will return to work tomorrow morning."
He says negotiations have gone backwards.
"The company arrived at the mediation with a whole new set of claims and demands, some 70 pages of material, most of it which we hadn't seen before. So that came as a bit of a surprise to us and set the negotiations back to about where they were at the beginning of the year."
AFFCO says further bargaining talks have been set up for Monday and Tuesday next week.
An Employment Court hearing on the legality of the lockout has been set down for 16 May to run for five days.