Sixty-four thousand birds are to be slaughtered at a commercial poultry unit in Co Tyrone after the discovery of a suspected case of bird flu.
Stormont's Agriculture Department has put disease control measures in place and sent samples off for confirmation.
The suspected outbreak was discovered near Dungannon.
A Temporary Control Zone (TCZ) has been put in place pending the results.
If confirmed, it would be the first outbreak in a commercial flock this year following confirmation of several incidents in the wild bird population.
The poultry industry is worth £600 million (€720m) to the Northern Ireland economy which is heavily reliant on the agri-food industry.
An Avian Influenza Prevention Zone (AIPZ) has applied across Northern Ireland since mid-January, requiring strict biosecurity measures to be applied.
A mandatory housing order for all poultry is due to take effect from midnight tomorrow.
A similar order has been issued in the South.
The head of the National Disease Control Centre at the Department of Agriculture has warned that the housing order should be taken very seriously.
There has been ongoing contact between the agriculture departments on both sides of the border as the authorities contend with a potential outbreak.
Stormont's Chief Vet Brian Dooher said the disease control measures had been taken to prevent onward transmission of the disease - known formally as Highly Pathogenic Avian Influenza (HPAI).
"I appeal to all bird owners - backyard and commercial - to take all necessary steps to protect your flock. This includes ensuring continuous excellent levels of biosecurity and adhering to all the requirements mandated under the AIPZ," Mr Dooher said.
"Samples from the infected premises have been sent to the National Reference Laboratory to confirm strain and pathogenicity. Should HPAI be officially confirmed, these TCZs will be revoked and replaced with a three kilometre Protection Zone (PZ) and 10km Surveillance Zone (SZ)."
The Head of Disease Control at the Department of Agriculture said he is concerned by the detection of bird flu at the poultry farm.
Speaking on RTÉ News, Dr Eoin Ryan said "a lot of the poultry industry is concentrated there, and there are many, many jobs at stake.
"The risk really is of spilling the virus over, spilling from the wild bird population into poultry flocks in that area, and that's why it's really important to take keep birds indoors and do everything possible to protect against the risk of inadvertently bringing in virus.
"So for instance, no necessary visitors onto the farm, no sharing of equipment between farms.
"Have separate clothes and footwear for going into the birds and use disinfectant on the footwear."
"These are the actions we're really strongly urging people to take, and that's the best way we can protect the poultry industry, particularly those border areas, Cavan, Monaghan, etc, and protect those jobs," he added.
Dr Ryan said the housing order is a necessary step for reducing the risk of bird flu spreading.
"All poultry, that's chickens, ducks, turkeys, have to be brought indoors for their own protection, to keep them away from coming into contact with wild birds which may be infected," he said.
The expert repeated advice to the public not to approach or touch wild birds who are sick, dying or dead.
Additional reporting: Colman O'Sullivan
