Nearly 800 staff in Haydock began a 24-hour walkout at 0000 GMT on Monday.

The workers voted to take the action because the supermarket chain's hourly pay rates are lower than those of workers with similar firms in the region.

But Sainsbury's said it did not expect the walkout to affect customers in its supermarkets.

Staff - most of whom are members of shopworkers' union Usdaw - are angry the current �5.75 an hour has not been increased to the regional average of �8 an hour, but to �7.55.

The action at the depot - which supplies Sainsbury's stores across northern England - is due to end at 2359 GMT on Monday.

A spokesman for Usdaw said negotiations, which have been going on since last March, had been "exhausted".

"In 2002 Sainsbury's recognised they were paying below the market rate for warehouse staff in the region," he said.

'Contingency plans'

He said Sainsbury's had initially pledged to increase pay rates to �8 an hour in 2004.

"They have broken their promise," he added. "Most warehouses are paying �8 an hour."

He said the firm had taken the stance despite workers agreeing to new working practices.

However, Sainsbury's said negotiations with Usdaw were still continuing.

A spokesman said: "Customers will not notice any difference in store. We have contingency plans in place.

'Competitive package'

"Haydock is one of 20 depots and we are able to move product throughout the network.

"We are offering a very competitive performance related package which, compared with competitors, is one of the best in the area.

"In addition we have given an above inflation pay rise for the last three years. We hope to continue discussions with Usdaw after Monday."

Usdaw said it is prepared to continue the negotiations with the company.