About 75 jobs are at risk after the company which owns the News Letter decided to close two printing presses in Belfast and in the north west.
Johnston Press bought the News Letter last September
Johnson Press said it would consult affected staff, who would be redeployed or offered voluntary redundancy.
The Scottish-based media group is one of the largest publishers of local and regional newspapers in the UK.
Peter Williamson of the union Amicus said the scale of the potential job losses came as a "big shock".
Managing Director Jean Long said the presses being closed no longer met the needs of advertisers and readers.
"It is therefore proposed to utilise printing facilities elsewhere in the group or at a third-party supplier, which will give our titles more colour and improved quality," she said.
Management, union representatives and workers met at the News Letter's Boucher Road headquarters on Tuesday to finalise redundancy plans.
The south Belfast operation is expected to close within two months.
The job losses are also expected to include 12 posts at the Derry Journal's printworks in Londonderry.
Last September, Johnston Press acquired Morton Newspapers, publishers of 17 weekly and five free titles.
In the same month, the company also bought Local Press Ltd., publishers of the News Letter and Derry Journal.
Johnston Press said the proposed closures followed a strategic review of its operations in Northern Ireland.