The chances that shoppers at Coles would find half-empty shelves at the supermarket giants' different outlets became higher as the strike at its Melbourne warehouse entered its fifth day on Friday.

The industrial action is expected to last longer despite the plan by Toll Holding, the operator of the facility to go to Fair Work Australia, after members of the National Union of Workers voted on Thursday to reject Toll's offer.

Toll offered to hike the salaries of its Somerton employees by 4 per cent a year, up from the previous 3.5 per cent offer. However, Toll removed other entitlements previously offered to the employees. The firm also insisted that the warehouse workers are paid 30 per cent higher than the award rate.

Toll said the industrial action is illegal and the blockade, which prevented trucks from entering and leaving the warehouse, is unsafe. However, the union said the ongoing strike showed the commitment of the workers in seeking fair treatment from Toll and Coles.

Coles said the industrial dispute has little impact on its stores. Trapped inside the warehouse are 46,000 pallets of food and alcohol, costing millions of dollars in grocery stock.

Amid the strike, Coles Managing Director Ian McLeod told the Australian British Chamber of Commerce lunch on Thursday that he expects the country's retail climate to remain tough and more competition as high-profile international retailers open operations in Australia. He cited the entry of Costco and Aldi.

However, he said Cole has no plans to go international at this time since its size is just right for the existing market.

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