If declared over, there would be a 60-day period before negotiations could be re-initiated, unless both parties agreed otherwise.
Until then individual agreements should be based on the collective agreement but the union says they are "completely different".
Union workers at three Affco meat works have signed individual agreements to ensure seasonal employment.
In July the union sought an injunction to prevent a lockout at Rangiuru. The court denied the injunction but said there was an "arguable case", to be heard in October.
"Wairoa workers have seen the impact of accepting the company's individual agreements in other sites and they've decided they won't put up with that," NZ Meat Workers Union organiser Eric Mischefski said.
"The workers know this isn't going to be easy.
The company will try to recruit other workers both locally and from other towns to replace them. But, in a small town like Wairoa, the workers have wide support, including whanau, hapu and iwi.
"Wairoa knows that it is important the workers at the freezing works do well or local businesses and the community pay the price."
Affco director of operations Rowan Ogg said he was surprised at the Wairoa action because a contract was a legal requirement before work.
Terms and conditions offered were "not dissimilar" from standard industry contracts.
Wairoa's last season was "one of the longest seasons, with the best earnings for many years" and Affco's changes to the collective contract would result in "longer seasons and better earnings for all employees".
Union workers from other sites supported the Wairoa protest by its 250 members.
A two-day strike planned for Affco's eight plants last month, after the company walked away from court-ordered mediation on the collective agreement, was called off and iwi leaders met Affco management.
Disputes at North Island Affco plants became common after the company was taken over by the Talley's six years ago.
A three-month Affco lockout in 2012 was resolved only after the Iwi Leaders Forum became involved.
Check out our video footage:
http://www.nzherald.co.nz/hawkes-bay-today/video/news/video.cfm?c_id=1503454&gal_cid=1503454&gallery_id=154098