NIPSA members who deliver supplies to hospitals and the community are to take part in a one-day strike today.
The trade union warned supplies - such as syringes - to hospitals including the RVH and Mater, could be impacted by the action from warehouse operatives employed by the Business Services Organisation at Boucher Crescent in Belfast.
NIPSA General Secretary Alison Millar last night said the workers were taking action following concerns about "working practices" at the site.
"It is disappointing that management have failed to address the real concerns of our members regarding the working practices in the BSO warehouse," she said.
Ms Millar said the "main issue at the heart of the dispute involves what is called a 'pick rate'".
"This involves the number of items forklift truck drivers have to retrieve each and every hour, every day of the week," she said.
"The rate set is unacceptable and unachievable and is a health, safety and welfare issue.
"Members have been threatened with disciplinary action if they fail to reach and maintain this pick rate."
The Belfast Trust last night declined to comment.
