Frozen food chain Iceland has announced its distribution centre in Flintshire will close at the end of September.
Iceland has shed over 300 jobs in Flintshire in the past year
About 350 jobs will go at the site, and the company will create a similar number at its new centre in Warrington, Cheshire, 23 miles away.
The company said a "significant proportion" of staff were interested in transferring to the new centre but some redundancies were inevitable.
A union spokesman said Iceland had rejected its cost reduction proposals.
The company employs several hundred staff at the company headquarters on Deeside.
The Transport and General Workers' Union (T&G) said the company had insisted on £2m in cost reductions through cutting pay and terms and conditions or they would move the depot to Warrington.
According to the spokesman, the union had put forward a number of plans including proposals earlier on Tuesday which would achieve the £2m target.
He added over 250 driver and warehouse staff jobs were now affected and a 24-hour strike starting from midnight on Thursday was a possibility.
Further talks over redundancy terms are taking place on Wednesday.
Iceland's chief executive Malcolm Walker said: "We have taken the decision to close Deeside with considerable reluctance, as the result of our failure to achieve agreement with the trade union on wages and working conditions that would have made it viable.
"Deeside is one of four Iceland depots in the UK, and is by far the least efficient and most expensive to operate."
In March, Iceland shed 80 call centre jobs at its Flintshire headquarters and made 400 staff redundant the previous year.