More than 170 workers at a glass bottle factory in Cheshire have announced plans to strike next month, leading to United to warn of shortages because of the dispute over working patterns and contracts.
A total of 12 days of strike action have been announced by union members at ENCIRC in Elton with the first 48 hour strike beginning on Thursday, May 6.
This will be followed by a further 48 strike beginning on Thursday, May 13.
Later in the month there will be two four day stoppage beginning on Wednesday, May 19 and Wednesday, May 26.
Unite has said the dispute involves workers in ENCIRC’s glass manufacturing section who believe that they are being treated in a less favourable manner compared to the company’s other departments.
When contacted for comment by BusinessLive, a spokesperson for ENCIRC said it had offered union members a proposal to reduce their average working week but boost their pay - which was rejected.
The firm added it will continue to work with employees to find a "viable, fair solution".
A Unite statement said: "Over 170 workers were balloted for industrial action, as the introduction of flexible working practices has resulted in an insufficient pay uplift, the loss of flexibility when annual leave can be taken and a reduction in staffing levels giving rise to health and safety concerns.
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"The strike action is set to lead to a major disruption to ENCIRC’s business and likely to cause a shortage of glass bottles for the company’s two major clients Diageo and AB InBev.
"Popular brands that will be affected by the strike include Budweiser, Yellow Tail wine, Baileys, Coors Light, Jameson and Pataks curry brand.
"Unite has sought to follow the existing dispute resolution process to resolve the industrial dispute, via the conciliation service Acas but the company has declined to discuss the core matters at the centre of the dispute."
The workers involved recorded a 95% yes vote in favour of strike action, the union added.
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"Unite regional officer Andrew Johnson said: "This dispute is about equality and fairness, workers in the glass manufacturing division are not being treated in the same way as workers in other sections of the company.
"If the strike goes ahead it will cause major disruption to the supply and distribution of major brands.
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"Given the overwhelming vote in favour of industrial action it is very disappointing and somewhat surprising that ENCIRC has not shown more determination to resolve this dispute and avert strike action.
"Unite’s members are taking strike action as a last resort because their concerns have been ignored.
"Unite believes that if ENCRIC is prepared to address the concern of members this dispute could be resolved and strike action avoided, even at this late stage."
An ENCIRC spokesperson said: "Our ambitious plans to reduce the average working week for everyone at ENCIRC with no detriment to pay come as part of our commitment to boosting workplace wellbeing.
"The vast majority of staff are now working a reduced week, and we’re looking at finding solutions to support the rest of our employees, including those in Glass Shift.
"Following a consultation with Glass Shift Union Members, we presented a solution which would have reduced their average working week, while also boosted their hourly rate of pay.
"The offer included an in effect 7% hourly pay increase, and followed an above inflation pay increase the previous year.
"However, this was rejected by the union members following a ballot. We will continue to work with Glass Shift employees to address their concerns with the aim of finding a viable, fair solution.
"We want ENCIRC to be a great place to work for everyone which is why we’ve also introduced a range of other benefits for employees across the business.
"These include better life insurance, private healthcare options, free workplace gyms, new training programmes, and more."