SIPTU says it is has been told at least 27 workers are to lose their jobs at the Liebherr manufacturing plant in Killarney.
The union says there is potential for up to 60 jobs to go in July and possibly a further 128 in August.
The firm employs more than 800 people making industrial cranes.
SIPTU Organiser, Joe Kelly, said his members were shocked and disappointed at the confirmation by the firm's management of the extent of potential job losses over the coming weeks and months.
He said: "This is a severe blow to the loyal Liebherr workforce, their families and the community in Killarney and surrounding areas. The company has provided steady employment for generations of workers in Kerry."
SIPTU representatives are due to meet company management on 26 June to discuss ways to reduce the number of job cuts and and to minimise the impact on those affected.
Liebherr which was established in Killarney in 1958.