About 40 workers picketed outside Pak'nSave Hastings on Saturday afternoon in an effort to get better pay.
Placards and loudspeakers urged public support for the protest, organised by First Union and held at midday, which was met with dozens of toots from passing vehicles.
First Union's cross-sector organiser for Hawke's Bay, Mike McNab, said union members had no choice but to take industrial action following failed negotiations with their employer.
"I'm very disappointed that it's come to this.
"The workers don't want to do this but they're not being heard.
"We are fighting back."
Union members, who were mostly on minimum wage, had requested a pay rise due to higher living costs including fuel and rent increases but this had been denied, McNab said.
"They're working hard, it's unfair.
"They don't want charity, they want to be paid fairly for their day's work."
Mediation had been agreed to between the union and Pak'nSave Hastings and was expected to be held on August 2, but McNab said he did not think a pay rise would be offered.
"We want him [Pak'nSave Hastings owner-operator Brendon Smith] to reconsider. We would like him to come back to the bargaining table with some money.
"The union is ready to negotiate at any point."
Saturday's picket was only the beginning and the union would "ramp up" activities unless the employer organised urgent mediation, he said.
"Pickets will continue if no outcome."
McNab said the first picket had been successful with lots of public support and he hoped Pak'nSave got the message.
Smith said the supermarket continued to engage in good faith with First Union in relation to collective employment agreement negotiations.
"We are a large employer in the area and we respect and value hugely the contribution made by our team.
"We believe we are at or above market with our employment terms and what's more, we provide substantial support to a wide range of organisations and community groups in the Hastings region."
Union workers spent their time handing out flyers, speaking to customers and making their voice heard with slogans such as "we want fair pay, when do we want it? Now" as well as carrying placards during the picket outside the supermarket on the corner of Heretaunga St West and Charles St.