Affco's appeal to the Supreme Court, over a long-running battle with the Meat Workers Union in Wairoa, has been dismissed.
The dispute started after negotiations for an expired collective contract broke down.
Affco was the first employer to end bargaining under 2015 amendments to the Employment Relations Act, which allowed firms to opt out of multi-employer agreements and removed the duty, under good faith bargaining, for both sides to reach agreement.
Workers who refused to return to a new season on individual contracts in 2015 were locked out for five months.
The Employment Court ordered the union members return to work, but upon their return they found their terms and conditions were very different.
After a compliance notice was issued to Affco the workers were employed according to their collective agreement.
Affco took the case to the Court of Appeal which upheld the Employment Court decision that the lockout was unlawful. The Court of Appeal said Affco sought to fragment future bargaining strength of the workforce by isolating individual workers.
Earlier this year Affco's application for a judicial review of the Employment Court decision was thrown out by the Court of Appeal, which described the application as "an abuse of process" ahead of the Supreme Court hearing.
The Supreme Court judgement said the essential question was whether the workers who presented themselves for work in 2015 were employees at the time, under the Act.
The union argued the reference to security of employment in the collective contract showed a long-term relationship.
Affco lawyers highlighted terms such as "layoffs and re-employment" for new seasons.
The judgement said employees under the act included people seeking work.
"As we have emphasised, the second respondents [union members] in this case were not, in contractual terms, strangers to the employer. Rather, they were people who had previously worked for Affco and to whom Affco owed contractual obligations, including as to re-hiring, even though their employment had terminated at the end of the previous season and they were seeking to be re-engaged for the new season.
"That feature of termination plus re-engagement under the umbrella of a number of continuing obligations distinguishes this case. Like the Court of Appeal, we consider that the relationship between Affco and the second respondents was sufficiently close to bring the latter within the scope of the word employees."