Some 150 of the Stirling-based company's 275 staff went on strike 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 were due to come into effect from 29 August.

Norman King, regional political officer for Unite, said that strike action was ongoing, with the next planned for 29 June.

King said: "The staff are striking over a change in working priorities after no agreement was made at the end of a consultation period.

"It means that staff will be expected to work longer for less money. Some staff will also be £27 a week worse off."

He added that other detrimental changes included changes to sick pay and holiday entitlement, and that UCP had taken out a court injunction to try to stop the strike.

King said the Court of Session in Edinburgh, which heard the case, awarded costs against the company, which gave the union the right to go ahead with the strike.

"Unite is just trying to get a satisfactory solution to the changes implemented by the business," King added.

UCP declined to comment.