Recruitment firm Cpl has said key sectors in the Northern Ireland economy could lose jobs to the Republic unless reassurance is given on the status of EU workers.
he firm, led in Northern Ireland by Aine Brolly, said agri-food in particular could lose out if it can no longer rely on EU workers. And she said firms were already losing out as they couldn't recruit enough people.
Around 70,000 people work in the agri-food sector, which contributes around £1bn to the economy every year.
In the run-up to the EU Referendum, poultry giant Moy Park, which employs large numbers of EU workers in its NI plants, said future access to labour was one of the "compelling reasons" why it was in favour of staying in the EU.
And export growth in agri-food is outperforming the rest of the UK, Cpl said, with 6% growth to £7.4bn last year.
Chief executive Ms Brolly said continued access to a EU labour pool should be a priority to avoid Northern Ireland losing out.
"EU workers form a vital part of our economy and with the uncertainty and changing social dynamic following Brexit, as well as the fall in sterling, businesses are struggling to recruit the number of EU nationals needed to support development," she said.
"The agri-food industry is reliant on EU workers who make up 90% of its employee base, often on temporary contracts due to the seasonal nature of work and this flow of workers has to be maintained to ensure the continued growth of the sector."
Ms Brolly said temporary workers across the UK - from fruit pickers to IT consultants - had grown to around 865,000.
"Should future policy restrict access to this non-UK labour pool, then the agri-food industry will face a significant challenge," she said. "The industry would become less competitive and could decline as a result and more labour intensive jobs here may end up relocating to the south of Ireland, where there would still be access to a wider EU labour pool.
"Northern Ireland is the most exposed region of the UK regarding this issue, given the nature of the all-island economy and all-island businesses operating here."
Meanwhile, UK employment group Reed has said half of employers now believed that leaving the EU will hit work, compared with 70% in the weeks following the referendum last June.
A survey of more than 440 businesses found that a third predicted that the outcome of the UK's departure from the EU will be positive, with more jobs and lower unemployment.
Chairman James Reed said the number of jobs being advertised by the group backed up the optimism, with almost 700,000 new positions on offer this year, up by 10% on a year ago.
Concerns remained among employers, including the possibility of an economic downturn and work being moved abroad.
A majority of employers said they have not made changes to their recruitment since the vote to leave, indicating British businesses have held firm and continued with recruiting plans.