Union Unite said in a statement that the action began at 6am today (14 August) and is due to end at 5.59am on Monday 11 September.

Unite had postponed previous planned strikes to hold further talks and seek an agreement. However, workers rejected the company’s latest offer.

Cepac offered an 8% pay increase “but with significant detrimental conditions including longer hours, lower overtime rates and a change in shift patterns”, according to the union.

“Industrial relations have further deteriorated as Cepac has said that if members do not agree to the inferior conditions, then it will impose them on the workforce,” the union further stated.

Unite general secretary Sharon Graham said: “Cepac’s pay offer has more strings attached than an orchestra, there is no way our members will accept worse conditions. This is a wealthy company that can fully afford to make a fair pay offer but is instead trying to cut terms to boost profits.

“Unite does what it says on the trade union tin and always puts the jobs, pay and conditions of its members first. The workers at Cepac will receive the union’s complete support.”

Unite said the action would mean that some of the UK’s largest food and drink outlets would likely face packaging shortages.

Cepac produces corrugated packaging and serves clients including HBCP, whose customers include Greggs, Costa, Subway, and Pret, along with C&D Foods Group, whose customers include Aldi, Tesco, Morrisons, and Asda. Other customers include Mars, Carlsberg, Innocent Drinks, Pernod, Lidl, Sainsbury’s, and Diageo.

In response to a request from Printweek to comment, Cepac group managing director Steve Moss said the strike action was very harmful to the business and its customers and that the notification of an initial two weeks of strike action with a further two weeks now added was particularly disappointing.

“The company has continued to present alternative and improved offers to Unite who have failed to fully and realistically engage with the company on these offers. The pay awards on offer range from 8% to 17.5% dependent upon individual roles with a focus on transforming the business to become a profitable centre of excellence for sustainable packaging.

“Along with the generous pay awards offered, the company is seeking to make some minor changes to terms and conditions, including a small increase in working hours for some employees. These changes are an essential part of the plan to increase productivity to ensure future growth and investment at Darlington. It is sad that Unite seem unable to engage positively to ensure the future of the employees at the Darlington site.’’

Moss explained that the impact of industrial action would jeopardise the immediate plans to invest and secure the future of the business at Darlington.

“The Darlington site has a promising future with a significant market opportunity in sustainable packaging. We will still seek to commit investment, develop the business and protect livelihoods, given a willingness to co-operate on the part of the union.”

“Regrettably the company is forced to continue to evaluate any negative financial impact on an ongoing basis and the escalation to an all-out strike for four weeks only emphasises the urgent need for this evaluation.

“The uncertainty regarding production heightens the risk that Unite’s action will seriously damage the business. We shall of course continue to take actions to seek to minimise disruption to our customer base. We have already been forced to postpone significant investment projects due to the adverse impact of the uncertainty created by this industrial action and to relocate new machinery elsewhere in our group.’’

Moss added that customers and suppliers had continued to be “extremely supportive” of the company and work with Cepac through this period of disruption. He said the business would do all in its power to ensure continuity of supply.

He also commented on the impact that threatened escalation was likely to have on pay increases now and in the future.

“The escalation and strike action threatens the stability and future of our business. We are urgently reviewing the potential financial impact of the industrial action. However, it is likely to impact the affordability of the pay offers that are currently still on the table for discussion and the company’s ability to pay them.”