Staff at Sunderland's Liebherr crane plant are to walk out in a row over pay.
Workers at the Deptford factory will be striking for two days next month in a dispute over what unions bosses say is an ‘inadequate’ offer.
Company bosses have defended the offer, which has been accepted by staff who are not part of the union negotiating unit.
Twenty-eight skilled crane assemblers will strike from 7.59pm on Thursday, August 9, until 11.59pm on Friday August 10, and again on August 16-17.
The action is in addition to an existing overtime ban.
Union bosses from Unite will be coordinating the industrial action with the GMB union, which also has members at the Deptford Terrace site.
The union says Liebherr Group's website reports the firm has its the highest turnover in its history – a total of €9,845 million (almost €10 billion).
Unite members voted by 79 per cent for strike action after rejecting the company’s offer of three per cent, a £150 lump sum and an extra day off over the Christmas period for the year starting January 2018.
Unite regional officer Mark Sanderson said: "While the company’s offer may appear reasonable, it has to be seen in context of past pay deals.
"In recent years, our members have accepted below inflation pay awards as the management said that business was not so good, but that when things picked up, there would be higher pay rises.
"Our very experienced members, who have contributed to the highest turnover in the Liebherr Group’s history, now want the firm to come good on its past promises and offer a generous pay rise to make up for the years of below inflation increases.
"Our members take great pride in the high quality cranes they assemble for the oil and maritime industries, but feel that ‘enough is enough’ and that the current offer is inadequate.
"Unite’s door is open 24/7 for genuine pay talks with the management before next month’s strike action."
GMB organiser Keir Howe said: "Our members have worked extremely hard to support the company and given that the Liebherr Group achieved its highest ever turnover in 2017 and
locally Sunderland showed a good profit, our members want to be rewarded."
"The offer is below RPI inflation and over a number of years members earnings haven’t always kept pace, leaving them worse off as living costs rise."
Liebherr managing director Ralph Saelzer said the unions were demanding a four per cent pay rise at a time when CPI inflation was just 2.4%.
While Liebherr Group as a whole was doing well, the maritime cranes operation was facing tough competition, he added.
"We fully acknowledge and respect the recognised unions GMB and Unite the Union as the legitimate representation of the bargain unit and welcome the in general positive and fruitful cooperation," said Mr Saelzer.
"Our offer is fair and adequate and has been put forward in full recognition of the efforts and commitment of our employees and despite the difficult business conditions in a very competitive market for our maritime crane products.
"Furthermore the offer is well above average pay-reviews in the region and nationwide (average 2.5% over last 3 months (EEF data)) as well as the CPI inflation rate.
"The offer is in line with the pay review at our sister company in the UK.
"Staff members outside the bargain unit have accepted our offer in an independent ballot because it is seen as fair and adequate.
The firm rejected the claim that pay offers had been below inflation in recent years, he added.
Last year had seen a two per cent rise, compared to inflation at 1.8%, while 2016's pay deal had involved a 2.3% increase, at a time when CPI was 0.3%, combined with a reduction of working hours per week from 39 to 38, which increased the plant's wage bill because of the need for increased overtime and/or additional staff.
A pay rise of 2.3% had been awarded in 2015, when CPI was 0.5%, and weekly working hours reduced from 40 to 39, and 2014's increase had been 2.8%, compared to a CPI of two per cent.
One member of staff, who did not wish to be named , said he was happy with the pay offer as it stood and concerned about securing the long-term future of the plant: "I am worried fotrthe young people coming through," he said.
"I think it is better to do things without threatening and taking money out of people's pockets."