Check your $100 bills, says a major supermarket operator, as the company discovered counterfeit notes during the counting of its day's takings last week.

The Frankie Company Ltd has warned the public to be on the alert for $100 fake notes and posted a notice on social media stating that Frankie discovered counterfeit $100 notes on Friday.

"To all businesses and money transfers (MoneyGram), please be extremely careful and double-check all $100 bills before completing transactions," the supermarket said.

Frankie reminded the public, especially businesses, that in order to spot a fake note, it is important to take a good look at the bill and see if it's not faded compared to the real polymer notes.

Moreover, it is also important to check the clear window and the watermark of Malietoa Tanumafili II.

"If it feels like paper rather than plastic, it's likely fake," the company said.

"Please stay vigilant, we've just discovered counterfeit $100 notes being used today (Friday) at Frankie.

"These fakes are becoming harder to spot at first glance, but they can cost your business or your family dearly if you accept them." 

Frankie Company urged members of the public to share this notice so that businesses and individuals will be aware and be on the alert.

Last year, a rental car company owner shared his frustration with a customer who paid for her rental car with fake $20 notes.

He also warned other businesses and people to be aware of it and to know the differences between a real and fake $20 bills during any transaction.