Coles is at the centre of more consumer outrage, after introducing a trial ban on trolleys at its self-serve checkouts.

The supermarket giant confirmed on Wednesday that it is trialling “baskets only” in self-service queues in about 20 shops across the country. That means anyone with too many items for a basket will have to wait in line at a full-service checkout.

A Coles spokeswoman said the trial was intended to tackle congestion at self-service checkouts.

“Assisted checkouts are a preferred choice of checkout for many customers and offer convenience and efficiency in their shopping experience,” she said.

“Team members are available to serve customers with trolleys in the main lane registers, and if there is not one vacant the store can open a register.”

The move comes just months after Coles sparked customer anger with its repeated changes of policy on single-use plastic bags – handing out replacements for free, then deciding to charge for them, then making them temporarily free again.

On Wednesday, consumers voiced their displeasure at the trolley ban.

Some said congestion problems at self-service checkouts were often due to the extra time needed to set up re-usable bags, and frequent “errors” in the checkout machines. Errors require staff to override the machines if they fail, for example, to register the correct weight of items.

Other customers said they chose self-service checkouts for convenience because a lack of staff at full-service checkouts meant delays.

One Coles customer said they had been told the trolley ban was designed to crack down on theft, News Corp reported.

“Perhaps there should be no customers, with Coles taking away staff and now trolleys,” one Twitter user wrote.

“Maybe they could make sure that all the empty checkouts are staffed, then we won’t be forced to take trolleys through to serve ourselves,” another said.

Coles refused to reveal the exact location of the stores involved in the trial, claiming it did not have access to that information.

@Coles I know you are trying to make improvements to services but when a store only has 3-4 staffed registers including the service desk it's not feasible to ban trolleys from self service. You brought them in to let go so much service staff now you want to punish trolley users?

— Neil (@neil1954) September 18, 2018

https://twitter.com/pklower/status/1042175357380513792

In principle I agree with @Coles trialling no trolleys in self check outs as these should be fast check outs but they don’t have enough manned checkouts in their bid to cut staff costs. Can’t have it both ways.

— Tony 🇦🇺🇺🇦 (@tonka9754) September 18, 2018

https://twitter.com/News_Listener/status/1042189925473386496