Affco is appealing an Employment Court ruling that it unlawfully locked out Wairoa workers during collective bargaining talks.
Affco was the first employer to test amendments to the Employment Relations Act, which let firms opt out of multi-employer agreements and removed the duty under good faith bargaining for both sides to reach an agreement.
In February the Employment Court ordered Affco to reinstate 160 Wairoa union members to their normal shifts and recognise seniority after they were locked out for almost six months.
It said they were locked out unlawfully without the required notice and the company undermined the collective bargaining process by sidelining the Meat Workers Union.
The dispute started when the NZ Meat Workers Union and Affco failed to renegotiate a collective agreement that expired in 2013.
The union sought a nil wage increase and for the agreement to roll over.
Company changes included removal of a seniority clause, which gave workers with the greatest experience first refusal of jobs at the start of a new season.
The company walked away from negotiations, citing the act's new amendments.
Leave was granted for the appeal on three questions of law: was the Employment Court wrong in finding workers were on employment contracts of indefinite duration, was it wrong to say the Employment Relations Act applied even if there was no relationship between company and workers in the off-season and was it wrong to say Affco's new individual employment contract did not comply with the law.
A date has yet to be determined for the hearing in the Court of Appeal.