Food manufacturers in Ireland have warned that rising production costs - particularly increased energy prices - are threatening jobs and could force the closure or relocation of plants.

Green Isle, which is part of Northern Foods and has five Irish plants employing more than 1,000 workers, has written to Irish energy regulator Tom Reeves, who approved 20% and 30% hikes in electricity and gas prices, warning that increased costs posed "a major problem" for the company. "We come under intense pressure every year from retailers in both the UK and Ireland to cut our costs to maintain business."

Because of high Irish costs, it said, it had been forced to close one Irish plant this year, transferring production to the UK, with the loss of more than 70 jobs.

It said the latest increase in electricity charges would "force us to review our remaining manufacturing plants, with more than 1,000 people employed, and consider transferring more production to the UK, where energy costs are more than 20% lower".

Jobs are also under threat at Cadbury Ireland, which employs 1,500 staff in Dublin and Kerry, as it struggles with rising production costs, including energy prices, pay and pension commitments.

The company was discussing restructuring with unions, a spokesman said.