The Canadian National Exhibition has opened in Toronto amid a labour dispute involving hundreds of workers.

Visitors were greeted by picket lines as the annual event that runs for two weeks got underway.

About 400 workers, represented by the International Alliance of Theatrical Stage Employees union, were locked out by the CNE's board of governors on July 20, after months of bargaining.

The board has said it wants to update the workers' contract to reflect the "highly competitive" marketplace and that it thinks the dispute should be settled at the bargaining table rather than in arbitration like the union has suggested.

The union has said the board refuses to bargain in good faith and that its workers will continue to picket through the duration of the CNE if the dispute isn't resolved.

The CNE is encouraging visitors to take public transit to get to the event's grounds.