UP to 110 electricians and fitters at six Murray Goulburn (MG) sites in Victoria, including Rochester, went on strike on Wednesday.
Members of the Australian Manufacturing Workers Union (AMWU) and the Electrical Trade Union (ETU) downed tools from 6am Wednesday morning for an indefinite stoppage.
The action followed a 24-hour stop-work on July 4 and a continued ban on overtime over enterprise agreement negotiations between the AMWU, ETU and Murray Goulburn.
ETU branch organiser Peter Mooney said there were three "contentious areas" in the negotiations.
"The first is a claim in regards to redundancies - we believe MG is creating a second class of employee by placing a cap on people's redundancies," he said.
"The second is a disagreement over apprentice numbers.
We have to put pressure on the company to show them we are serious.
"Murray Goulburn has indicated they are willing to hire three for their entire system, but even at their biggest site at Leongatha there will be no apprentices."
The third point was regarding wage increases, with the ETU believing the increase was below the the consumer price index (CPI) of 2.9 per cent.
Mr Mooney said it was unfair workers at other dairy production companies could receive $100 more than at Murray Goulburn.
He said the delegates would engage in a phone hook-up to determine whether the action would continue into Thursday.
"We don't want to take industrial action, but we have to put pressure on the company to show that we are serious," he said.
The parties began negotiations on April 28 and have since held seven full-day meetings to discuss the new enterprise agreement.
In a letter to employees dated July 14, Murray Goulburn general manager of manufacturing and supply chain Mark McDonald said wage increases would be above CPI, at 3.5 per cent per year over three years.
"This is an increase that is well above CPI and the average enterprise agreement wage rises in the manufacturing industry (3.1%)," the letter said.
"Whilst the offer includes the introduction of a cap on redundancy pay at 136 weeks, employees who currently have an entitlement over 136 weeks will have that amount honoured in the event that they are made redundant."
The redundancy cap of 52 weeks would only apply to new employees, according to Mr McDonald.
He wrote the industrial action was "unnecessary and unjustified".
"We are very disappointed that your representatives have still not endorsed this offer," the letter said.
"As a result of this industrial action, Murray Goulburn will need to continue to make alternative arrangements in order to mitigate the impact on our business and employees."