Workers at Smithfield Foods' meat packing plant in Tar Heel, North Carolina, have voted to unionise.

Employees at Tar Heel, the world's largest meat packing plant, will be represented by the United Food and Commercial Workers International Union (UFCW) and will enter into collective bargaining agreements with Smithfield.

The US meat giant and the UFCW union have fought a protracted 14-year battle over whether the Tar Heel workers want union representation, with both sides accusing the other of utilising underhand tactics such as election rigging and smear campaigns.

Workers voted 2041 to 1879 to join the union.

"When workers have a fair process, they choose a voice on the job," said UFCW director of organising Pat O'Neill.

"This is a great victory for the Tar Heel workers. I know they are looking forward to sitting down at the bargaining table with Smithfield to negotiate a contract."

Workers at 26 Smithfield-owned facilities in the US already have UFCW representation. According to Smithfield's annual report, prior to the Tar Heel vote, 28,800 of Smithfield's 58,100 employees were unionised.