Short-time working is to be introduced at Tayto's plant in Terenure, Dublin, because of a downturn in market expectations. The company's Coolock plant, which employs about 270, is to close for a week
The closure will be a "one-off", the company says, while the short-time working in Terenure is envisaged as a short-term measure.
A spokesman said job losses were not on the agenda.
Nearly all of the 127 employees at Terenure will be affected by the measure, which is likely to involve a three-day week every third week. Staff are to continue to work five days in the intervening weeks.
Mr Brian O'Neill, SIPTU's food branch secretary, said workers had opted for the three-day week over alternatives, at a general meeting on Monday.
A four-day week had also been suggested but, unlike the three-day option, this would have carried no social welfare entitlements, he said.
A spokesman for Tayto, which is owned by the Cantrell & Cochrane (C&C) group, said a slowdown in the snack-foods sector had hit the non-core products manufactured at the Terenure plant.
The company remained profitable, he stressed, but, like all of the players in the sector, it had to tailor its growth expectations over the past year.
There had been a build-up of stock levels at the Coolock plant and this would be dealt with by a week-long closure beginning on St Patrick's Day.
The spokesman acknowledged that increased competition in the sector, through slick marketing of imported brands such as Walkers crisps, had also had an effect.
"But the competition has been there for some time. The big issue is the fact that the entire market is facing a slowdown in the rate of growth," he said. "This is a short-term measure to address that."
He added that Tayto continued to maintain a strong lead over its rivals in the snacks sector, with its products, including King crisps, maintaining a 40.5 per cent share of the market, according to the most recent figures.
Tayto, which was established in 1954, was acquired by C&C in 1999 for £67.7 million (€86 million).
