Around 150 of the Stirling-based company's 275 staff will walk out today and again on Saturday after no agreement was reached during a consultation period.
According to Unite, UCP, which prints and manufactures packaging for the drinks industry, increased employees' contracted hours by five hours per week for no extra pay.
The union said that the new contracts would come into effect from 29 August. Norman King, regional political officer for Unite, said staff were currently "up against it".
He said: "Talks could have taken place today but the company wanted both sets of strike action called off for that to happen. Our members were willing to do that if these new contracts were changed but that hasn't been possible.
"It means that staff will be expected to work longer for less money. Some staff will also be £27 a week worse off."
Have your say in the Printweek Poll
Related stories
Latest comments
"I have worked in quite a few print sectors, including Walstead in the past. It is all tough, but most will not be surprised that the packaging sector is still growing. However, the service in the..."
""longer run litho work had “now returned to the Far East”?
Is this happening a lot?"
"Thanks Jo, look forward to reading it in due course. Administrators generally argue that they need to act with lightning speed in order to protect the business/jobs, thereby overlooking the fact that..."
Up next...
Revenue up to £3.2m, profits quadupled
Footprint picks up pace of acquisition strategy with Swindon’s C3
Controversy emerges over relationship with potential suitor
National World shares soar on takeover approach
24/7 access for customers
Bakergoodchild launches new SaaS platform
Strategic move for global growth