Up to 95 jobs could be lost at Wrightbus in Ballymena.
The bus manufacturer has confirmed that it has begun a statutory consultation process "regarding a potential workforce reduction".
In a statement it said it was "currently experiencing challenging market conditions".
In October Wrights Group announced a turnover of £264m. The company employs 1,700 people worldwide - with around 1,200 employed in Ballymena at its Galgorm plant.
William Wright, the 90-year-old founder of Wright Group was knighted in the New Year Honours list.
BREAKING: News emerging of nearly 100 redundancies at Wrightbus in Ballymena. Workers called to a meeting, Union will issue statement within next hour pic.twitter.com/GHGgLGkMQb
— Irish News Business (@irishnewsbiz) February 12, 2018
Unite the Union Regional Officer George Brash said the news "comes of the blue to our union" which had been told "there were likely to be line changes due to a shortage in parts but we didn’t expect any job losses".
Mr Brash said it was the latest hammer blow to the Ballymena and Antrim workforce."Wrightbus is one of the last major remaining employers in the area after a spate of site closures over the past two years."