Bankcards: One swipe and $150 in your account is frozen, sometimes for days

If you are paying for gas at an unmanned petrol pump, be aware.

One swipe of your credit card, and someone literally takes a hold of $150 in your account.

Several companies use the practice - which is legal - to safeguard payment for petrol.

But a woman who purchased $20 petrol from an unmanned petrol pump at Rotorua's Pak'N Save is angry she lost $150 worth of spending power for several days.

Sally Smyth said $150 disappeared from her credit card account despite the fact she had only bought $20 gas.

Pak'N Save owner/operator Neil Foster has defended the practice and said the money is put "on hold" rather than being deducted. Any delays in the money being returned to a person's credit card balance is the fault of banks - not Pak'N Save, he said.

Ms Smyth said she presumed the practice was to prevent drive-offs [without paying].

"I understand that it usually goes straight back in after the transaction but there are occasions when it does not."

Ms Smyth, who works as a graphic designer at the Daily Post, bought petrol on a Saturday, but didn't get the $150 back in her credit card account until a Wednesday afternoon.

There were no notices on the petrol pumps informing people of the practice.

"Everyone I have spoken to does not have a clue that this is what happens," she said.

Mr Foster said it was wrong to describe it as a "deduction" from someone's account - even a temporary one.

"It's basically a hold that is put on your card to that amount. I would not call it a deduction [because] the money is not physically taken out of your account ... we do it because if you come to pay for the fuel with no money in your account, it would obviously cause a problem."

It had been a common practice among other fuel providers who had unmanned pumps, rental car companies and hotels for at least three years, Mr Foster said.

The confusion caused by the transaction had previously been well documented and was highlighted on the Fair Go TV series.

The $150 "hold" on the account was meant to be "released" as soon as possible but sometimes banks were not able to conduct such quick transactions, he said.

"The bank blames us when it is not our problem at all ... We only ever have a problem once every six to nine months along these lines."

Consumers' Institute chief executive David Russell was unavailable for comment but a statement on the Institute's website said it "is a lousy way to treat customers. Dipping into customers' credit card accounts without warning isn't acceptable or good for business".