Supermarket workers who are required to work through the Covid-19 outbreak lockdown should be paid more for doing so, their union says.

Supermarkets are one of the essential services allowed to continue to operate while most of the rest of the economy shuts down for at least four weeks.

They have introduced measures to help keep staff safe, such as Perspex screens to protect them, protective clothing. Stores are also limiting the number of customers they allow in.

But Tali Williams, retail secretary at First Union, said supermarket employees deserved to be paid more for their work during this period. Many are on low wages – although Countdown has pledged to move most of its staff to at least $21.15 an hour from this September.

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Foodstuffs agreements have to be made at individual store level because the co-operative has an owner-operator model.

Williams said the workers deserved to have the essential service they were providing acknowledged.

The union had had discussions with Countdown and expected a response early next week, she said.

"We urge publicly all supermarkets whether they are Foodstuffs or Countdown to increase worker pay to acknowledge the burden they are taking on in society right now. Many of the workers are on the minimum wage, particularly those that are no covered by a collective agreement. That needs to be addressed immediately."

She said the supermarkets were sending out the right messages about protecting staff, but whether the directive was enforced depended on individual store managers.

Workers who contacted Stuff said they were concerned at the risk they were taking on.

Foodstuffs head of corporate affairs Antoinette Laird said its teams felt a "huge sense of pride as they work hard to meet New Zealand's grocery needs at this time".

"They are immensely proud, and have been working tirelessly to make sure products are moving through the supply chain, onto the supermarket shelves and into the hands of our customers. Both co-operatives and the owners are incredibly grateful for the extra lengths our people are going to, and looking after our people and all that entails is a key part of that."

ABIGAIL DOUGHERTY/STUFF Supermarkets are limiting the number of customers they allow in stores.

Supermarkets have been put under pressure in recent weeks as customers stocked up for the lockdown.

Food and liquor spending on Monday was two-and-a-half times more than the same date last year.

The figures from Paymark, which runs over 100,000 Eftpos machines in New Zealand and handles more than 70 per cent of the country's payments, showed a big increase for pharmacies in spending as well.

At food and liquor outlets, which included supermarkets, $111 million was spent through eftpos on Monday – a one day spend that has only been beaten once, on Christmas Eve 2019, which was 157 per cent more than the same day last year.

Countdown has been approached for comment.