Workers plan to picket outside Pak'nSave Hastings every weekend until they get a pay rise.
More than 20 First Union members held a demonstration outside the Heretaunga St West store on Saturday afternoon for the second time in two weeks over unresolved pay concerns.
Union organiser Mike McNab said public support for the workers had been growing and they would be "ramping" up their efforts.
Pickets will be held from 11.30am on both Saturday and Sunday this weekend and will continue until the union members get a pay rise, McNab said.
Saturday's picket had been positive with good public support and several customers saying they would stop shopping at Pak'nSave Hastings, he said.
"I think we got the message across."
One woman at the picket, who did not want to be named, said she came up from Palmerston North to support the workers.
Her husband is a union organiser in Palmerston North and they wanted to help fight for a worthy cause, she said.
Lillian Kahukura said she came to the picket because she belongs to First Union but works for a different company. "I wanted to support our union members."
The workers needed to be paid fairly, she said.
"I'm surprised to see how much support it has got."
The first picket was held on June 16 because workers, most of whom were on minimum wage, could not afford rising living costs and wanted to be paid a fair wage for a fair day's work, McNab said.
He also said he was trespassed from the store last week for talking to members about the picket, which is illegal.
Mediation between the store and the union had been planned for August 2 but this has now been pushed back until August 14.
A Pak'nSave spokesperson said Pak'nSave Hastings owner-operator Brendon Smith would not be making any further comment on the picket but on Friday he said he was disappointed the union had chosen to picket when both parties had agreed a date for mediation.