The workers had also been suspended for the duration of their industrial action.
Speaking to Hawke's Bay Today, E tu organiser Laurel Reid said that was an "aggressive" move.
"They are not getting paid for striking anyway. It just shows the company isn't taking any notice. It's not a good message at all."
Mrs Reid said the workers were in "high spirits" and had received good support from the public as well as colleagues, some of whom had joined the picket after finishing other work at the processing plant.
She added that the Silver Fern Farms maintenance employees were about 10 per cent behind the average rate of pay amongst engineers and electricians in similar organisations in Hawke's Bay.
Workers voted unanimously to strike for three days from Wednesday.
Silver Fern Farms head of sustainability and communications Justin Courtney said the strike action would not have an impact on operations, adding the company would continue to work to resolve the situation.
"The company's offer to settle the negotiations with E tu made in mediation during December clearly stipulated that the back-pay component was only available if industrial action was avoided.
"This was clearly understood by E tu and the employees covered by the offer. The Employment Relations Act requires a suspension when workers undertake a strike such that they are not paid during their time off work.
"We will continue to work with the mediation service and the union to seek a resolution.
"The plant is still operating and processing stock as normal in what is an important time of the year for farmers."